Revert "[vm] Enforce that entry points must be annotated by default."

This reverts commit cb9ecbc3636aaa4e8c8301caa4bab2d903825bf3.

Reason for revert: causes failures during Dart->Flutter roll and on Flutter HHH bots (see comments on the original CL).

Original change's description:
> [vm] Enforce that entry points must be annotated by default.
>
> Changes the default value of the --verify-entry-points flag
> to true.
>
> Changes the default value for the check_is_entrypoint argument to
> to the Invoke/InvokeGetter/InvokeSetter flags to true. The mirrors
> library implementation and calls via vm-service explicitly pass
> false for this argument now.
>
> Add annotations as needed, such as annotating classes with
> annotated generative constructors. In some cases, the annotations
> were more general than needed (e.g., annotating with a no-argument
> entry point annotation when only the setter is needed), so make
> those annotations more specific.
>
> As this pattern is already common in downstream code, allow
> Dart_Invoke on fields as long as the field is annotated for getter
> access. (That is, calling Dart_Invoke for a field is equivalent to
> retrieving the closure value via Dart_GetField and then calling
> Dart_InvokeClosure.)
>
> TEST=vm/cc/DartAPI_MissingEntryPoints
>      vm/dart/entrypoints_verification_test
>
> Issue: https://github.com/dart-lang/sdk/issues/50649
> Issue: https://github.com/flutter/flutter/issues/118608
>
> Change-Id: Ibb3bf15632ab2958d8791b449af8651d47f871a5
> Cq-Include-Trybots: luci.dart.try:vm-aot-linux-product-x64-try,vm-aot-linux-debug-x64-try,vm-aot-mac-release-arm64-try,vm-aot-mac-product-arm64-try,vm-aot-dwarf-linux-product-x64-try
> CoreLibraryReviewExempt: adding/editing vm-only pragma annotations
> Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/363566
> Reviewed-by: Martin Kustermann <kustermann@google.com>
> Commit-Queue: Tess Strickland <sstrickl@google.com>

Issue: https://github.com/dart-lang/sdk/issues/50649
Issue: https://github.com/flutter/flutter/issues/118608
Change-Id: Idba168f77b0636a50ad93309e29dc9989cc1f388
Cq-Include-Trybots: luci.dart.try:vm-aot-linux-product-x64-try,vm-aot-linux-debug-x64-try,vm-aot-mac-release-arm64-try,vm-aot-mac-product-arm64-try,vm-aot-dwarf-linux-product-x64-try
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/391460
Auto-Submit: Alexander Markov <alexmarkov@google.com>
Reviewed-by: Tess Strickland <sstrickl@google.com>
Commit-Queue: Tess Strickland <sstrickl@google.com>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>