Use generic packageId placeholder in NU1704 example message

Author: sbomer

docs/reference/errors-and-warnings/NU1704.md

@@ -10,7 +10,7 @@ f1_keywords:
 
 # NuGet Warning NU1704
 
-> Package 'Xamarin.Essentials' 1.8.1 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 Consider upgrading to a newer version of this package or contacting the package author.
+> 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 Consider upgrading to a newer version of this package or contacting the package author.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