Extirpate FOLLY_NODISCARD in eden/fs/utils/ChronoParse.h +5

Summary:
`[[nodiscard]]` is now available in all of our compilers. This diff changes the code to rely on it directly.

Generated with
```
reset && xbgs -l FOLLY_NODISCARD | grep -v Portability.h | grep -v json | grep -v xplat | grep -v ThirdParty/ | grep -v third-party | perl -pe 's/^fbsource.//' | xargs -n 100 perl -pe 's/FOLLY_NODISCARD/[[nodiscard]]/' -i
```

Reviewed By: dtolnay

Differential Revision: D87101315

fbshipit-source-id: 0bd19e81a6f974002eb09fe04590bed2fc9229d1

Author: r-barnes

eden/fs/utils/ChronoParse.h

@@ -35,7 +35,7 @@ std::string_view chronoParseErrorToString(ChronoParseError error);
 /**
  * Parse a string to a std::chrono::nanoseconds duration.
  */
-FOLLY_NODISCARD folly::Expected<std::chrono::nanoseconds, ChronoParseError>
+[[nodiscard]] folly::Expected<std::chrono::nanoseconds, ChronoParseError>
 stringToDuration(folly::StringPiece src);
 
 /**