Reuse NU1703 for deprecated MonoAndroid warning instead of NU1704

Per PR feedback on NuGet/NuGet.Client#7229, reuse the NU1703 warning
code for the MonoAndroid deprecation scenario. The previous NU1703
for Xamarin.iOS never shipped, so the code is safe to repurpose.

Remove NU1704 doc and references from TOC and index.

Author: sbomer

docs/TOC.md

@@ -202,7 +202,6 @@
 ### [NU1701](reference/errors-and-warnings/NU1701.md)
 ### [NU1702](reference/errors-and-warnings/NU1702.md)
 ### [NU1703](reference/errors-and-warnings/NU1703.md)
-### [NU1704](reference/errors-and-warnings/NU1704.md)
 ### [NU1900](reference/errors-and-warnings/NU1900.md)
 ### [NU1901](reference/errors-and-warnings/NU1901-NU1904.md)
 ### [NU1902](reference/errors-and-warnings/NU1901-NU1904.md)

docs/reference/Errors-and-Warnings.md

@@ -46,7 +46,7 @@ NuGet supports the following configuration properties.
 | Invalid input warnings | [NU1501](./errors-and-warnings/NU1501.md), [NU1502](./errors-and-warnings/NU1502.md), [NU1503](./errors-and-warnings/NU1503.md), [NU1504](./errors-and-warnings/NU1504.md), [NU1505](./errors-and-warnings/NU1505.md), [NU1506](./errors-and-warnings/NU1506.md), [NU1507](./errors-and-warnings/NU1507.md), [NU1508](./errors-and-warnings/NU1508.md), [NU1509](./errors-and-warnings/NU1509.md), [NU1510](./errors-and-warnings/NU1510.md), [NU1511](./errors-and-warnings/NU1511.md) |
 | Unexpected package version warnings | [NU1601](./errors-and-warnings/NU1601.md), [NU1602](./errors-and-warnings/NU1602.md), [NU1603](./errors-and-warnings/NU1603.md), [NU1604](./errors-and-warnings/NU1604.md), [NU1605](./errors-and-warnings/NU1605.md), [NU1606](./errors-and-warnings/NU1108.md), [NU1607](./errors-and-warnings/NU1107.md) |
 | Resolver conflict warnings | [NU1608](./errors-and-warnings/NU1608.md) |
-| Package fallback warnings | [NU1701](./errors-and-warnings/NU1701.md), [NU1702](./errors-and-warnings/NU1702.md), [NU1703](./errors-and-warnings/NU1703.md), [NU1704](./errors-and-warnings/NU1704.md) |
+| Package fallback warnings | [NU1701](./errors-and-warnings/NU1701.md), [NU1702](./errors-and-warnings/NU1702.md), [NU1703](./errors-and-warnings/NU1703.md) |
 | Feed warnings | [NU1801](./errors-and-warnings/NU1801.md), [NU1802](./errors-and-warnings/NU1802.md), [NU1803](./errors-and-warnings/NU1803.md) |
 | NuGet internal warnings | [NU1500](./errors-and-warnings/NU1500.md) |
 | Signed packages warnings (creation and verification) | [NU3000](./errors-and-warnings/NU3000.md), [NU3002](./errors-and-warnings/NU3002.md), [NU3003](./errors-and-warnings/NU3003.md), [NU3006](./errors-and-warnings/NU3006.md), [NU3007](./errors-and-warnings/NU3007.md), [NU3009](./errors-and-warnings/NU3009.md), [NU3010](./errors-and-warnings/NU3010.md), [NU3011](./errors-and-warnings/NU3011.md), [NU3012](./errors-and-warnings/NU3012.md), [NU3013](./errors-and-warnings/NU3013.md), [NU3014](./errors-and-warnings/NU3014.md), [NU3015](./errors-and-warnings/NU3015.md), [NU3016](./errors-and-warnings/NU3016.md), [NU3017](./errors-and-warnings/NU3017.md), [NU3018](./errors-and-warnings/NU3018.md), [NU3019](./errors-and-warnings/NU3019.md), [NU3020](./errors-and-warnings/NU3020.md), [NU3021](./errors-and-warnings/NU3021.md), [NU3022](./errors-and-warnings/NU3022.md), [NU3023](./errors-and-warnings/NU3023.md), [NU3024](./errors-and-warnings/NU3024.md), [NU3025](./errors-and-warnings/NU3025.md), [NU3026](./errors-and-warnings/NU3026.md), [NU3027](./errors-and-warnings/NU3027.md), [NU3028](./errors-and-warnings/NU3028.md), [NU3029](./errors-and-warnings/NU3029.md), [NU3030](./errors-and-warnings/NU3030.md), [NU3031](./errors-and-warnings/NU3031.md), [NU3032](./errors-and-warnings/NU3032.md), [NU3033](./errors-and-warnings/NU3033.md), [NU3035](./errors-and-warnings/NU3035.md), [NU3036](./errors-and-warnings/NU3036.md), [NU3037](./errors-and-warnings/NU3037.md), [NU3038](./errors-and-warnings/NU3038.md), [NU3040](./errors-and-warnings/NU3040.md), [NU3042](./errors-and-warnings/NU3042.md), [NU3043](./errors-and-warnings/NU3043.md) |

docs/reference/errors-and-warnings/NU1703.md

@@ -12,12 +12,17 @@ f1_keywords:
 
 # NuGet Warning NU1703
 
-> 'packageId' was resolved as a dependency of 'project', but the dependency is using 'Xamarin.iOS' while 'project' is using 'net6.0-maccatalyst14.5' as its TargetFramework
+> Package 'packageId' 'version' uses the deprecated MonoAndroid framework instead of 'net6.0-android' or later. Consider upgrading to a newer version of this package or contacting the package author.
 
 ### Issue
 
-While `net6.0-maccatalyst` (and higher .NET versions) support using Xamarin.iOS dependencies, this is not guaranteed to be 100% compatible.
+A project targeting `net11.0-android` or later references a package whose resolved compile-time or runtime assemblies come from a `monoandroid` framework folder. The `MonoAndroid` target framework is deprecated in favor of `net6.0-android` and later .NET TFMs. While MonoAndroid class libraries might work at runtime, compatibility isn't guaranteed.
+
+This warning is only raised when both of the following conditions are met:
+
+1. The project targets `net11.0-android` or later.
+1. The SDK analysis level is 11.0.100 or higher.
 
 ### Solution
 
-Use a dependency that ships artifacts for `net6.0-maccatalyst` or a higher .NET version instead of relying on legacy Xamarin.iOS.
+Upgrade to a newer version of the package that provides `net6.0-android` (or later) assets. If no updated version is available, contact the package author and request that they update the package to target modern .NET Android TFMs.