This reverts commit c81711bdda.
Reason for revert: `Internal Error: Runtime type information not available for type_variable_local` - b/295131730
Original change's description:
> [dart2js] Add runtime type check for `await`.
>
> See https://github.com/dart-lang/sdk/issues/49396 for details.
>
> Fixes: #50601
> Change-Id: Ie89130cffe642b3e4935d7d02fe2e34f7fc8b12e
> Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/316320
> Commit-Queue: Mayank Patke <fishythefish@google.com>
> Reviewed-by: Stephen Adams <sra@google.com>
Change-Id: I481b119b6569d1bc9cf2ab80d997a3eb6d06f674
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/319421
Reviewed-by: Alexander Thomas <athom@google.com>
Auto-Submit: Oleh Prypin <oprypin@google.com>
Commit-Queue: Oleh Prypin <oprypin@google.com>