Remove duplicate FileDiffMigrationTests.

Review Request #7400 — Created June 9, 2015 and submitted — Latest diff uploaded

Information

Review Board
release-2.0.x
4d4f5fe...

Reviewers

Through some merge or something, we ended up with two versions of
FileDiffMigrationTests, one more comprehensive than the other. The
less useful of the two has now been removed.

Unit tests pass.