Revert "Reland "Add wrapper to normalize flags.""

This reverts commit bd33ce26202272177af6c52e195e7c13f0d1bf23.

Reason for revert: Breaks Android perf tests.

Original change's description:
> Reland "Add wrapper to normalize flags."
> 
> This is a reland of 642a49d1eb20b8c5744e745de79ddb585e0f7472
> 
> The change has the same effect but is now implemented through mb, rather than specifying a 'script', so that Android's special handling is not skipped.
> 
> Original change's description:
> > Add wrapper to normalize flags.
> >
> > Bug: None
> > Change-Id: I9d43602cc66198a29dbc0e7586d948ee76c5ec84
> > Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/145204
> > Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
> > Reviewed-by: Oleh Prypin <oprypin@webrtc.org>
> > Cr-Commit-Position: refs/heads/master@{#28532}
> 
> Bug: webrtc:10616
> Change-Id: I60ebd4891dbe8de18c653f8af88181ea966307de
> Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/145409
> Commit-Queue: Oleh Prypin <oprypin@webrtc.org>
> Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
> Cr-Commit-Position: refs/heads/master@{#28572}

TBR=mbonadei@webrtc.org,oprypin@webrtc.org

Change-Id: Ic0c6677b707397b03edd540a3fec1488d57cb70a
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: webrtc:10616
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/145728
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#28576}

tools_webrtc/mb/mb_unittest.py

@@ -453,11 +453,9 @@ class UnitTest(unittest.TestCase):
     self.assertEqual(files, [
         '../../.vpython',
         '../../testing/test_env.py',
-        '../../tools_webrtc/flags_compatibility.py',
         'base_unittests',
     ])
     self.assertEqual(command, [
-        '../../tools_webrtc/flags_compatibility.py',
         '../../testing/test_env.py',
         './base_unittests',
         '--asan=0',