[messages] Remove add_types_to_yaml.dart.

Now that this script has been used to add `type:` entries to the
analyzer-style `messages.yaml` files, and validation is in place to
ensure that future diagnostics have `type:` entries, the script is no
longer needed.

Change-Id: I6a6a69644fda49cbbaec643c8b3950d74be88d17
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/464245
Reviewed-by: Konstantin Shcheglov <[email protected]>
Commit-Queue: Paul Berry <[email protected]>

Author: stereotype441

pkg/analyzer_utilities/pubspec.yaml

@@ -21,6 +21,5 @@ dependencies:
 
 # Use 'any' constraints here; we get our versions from the DEPS file.
 dev_dependencies:
-  analyzer_plugin: any
   lints: any
   test_reflective_loader: any