[ddc] Fix legacy type in covariance bounds check
[ddc] Fix legacy type in covariance bounds check

There should be no way this could cause an unexpected failure
or break soundness but there is no reason to be marking the type
parameter as a legacy type in the check.

Change-Id: Ib4cf22cacd78d6cb9b55dd6ed594c75aa81ceead
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/149887
Reviewed-by: Mark Zhou <654f5fe0c4ca6c799b0e735dcf3fc1c389f35bf9@google.com>
Commit-Queue: Nicholas Shahan <03847abd2d8aadfe859ecb98095a31f9f515dc47@google.com>

dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk