Remove duplicate expectations

Removes cases of duplicate expectations. The expectation parser allows
cases of exact duplicates, but the UPF does not since it needs to know
which lines to remove/modify.

Change-Id: I319b240147324b83f6840be198a9948f9709f98e
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/218194
Reviewed-by: dan sinclair <[email protected]>
Commit-Queue: dan sinclair <[email protected]>
Auto-Submit: Brian Sheedy <[email protected]>
Commit-Queue: Brian Sheedy <[email protected]>