[gardening] Remove obsolete Flutter HHH patch

This change was submitted into Flutter/flutter already
(flutter/flutter@6f9ed76),
so removing this patch as it cannot be applied anymore and causes
Flutter HHH to fail.

Change-Id: Ic1b44f0ec0c85b9d343079f8a067cd59ebf37170
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/137040
Commit-Queue: Alexander Markov <alexmarkov@google.com>
Reviewed-by: Alexander Markov <alexmarkov@google.com>

Author: alexmarkov