Remove support for '///' multi-test marker
Remove support for '///' multi-test marker

Change-Id: I7d0341c758e547d457dbf4b60e1d5c7bf67bbb67
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/196483
Commit-Queue: Karl Klose <49bc0b76cffb0b10cd8c84f9cabc97a31ffe6343@google.com>
Reviewed-by: Bob Nystrom <afede3a9ebedb865bee78398feff6fbe97068f17@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