Remove unnecessary type annotation.
Remove unnecessary type annotation.

It seems that after switching to null safe version of package:html
we don't need it anymore.

Change-Id: I599ffb2e1b716358e07e4884544b62a2dfa72216
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/181461
Reviewed-by: Samuel Rawlins <5cf2cac5eec2ad6d0eb2b0f4ff6af9a590ce2bf6@google.com>
Commit-Queue: Konstantin Shcheglov <09e4d7516628963212bf4aace2f97603d2b706e4@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