Remove the old webtests.

We haven't maintained or even used the webtests in a long long time. The
more modern JavaScript unit tests are a better replacement for those
anyway. This removes the webtests from the codebase.

Reviewed at https://reviews.reviewboard.org/r/5878/
Don't strip leading slashes for perforce diffs.

Because perforce depot paths start with //, stripping a leading slash is a bad,
bad thing. I've moved the filename normalization into the diff parser, and
overridden it in the perforce specialization.

Testing done: Ran unit tests.

Reviewed at https://reviews.reviewboard.org/r/5879/