Remove unused helper classes Bug: angleproject:6954 Change-Id: I325f6a67b1f2f1dffdf051f83a8d4f29c4fe25dd Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/4628678 Reviewed-by: Roman Lavrov <romanl@google.com> Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>