Bug 139264

We have some code that "locks" tests in LayoutTests/perf, because they are timing sensitive, and would like to run on a separate thread. But this code is broken in several ways: 1. It doesn't do anything, because LayoutTests/perf is a leaf directory, and all these tests run sequentially even without locking. 2. It doesn't prevent other tests from running at the same time, so we have the timing problems that we were trying to avoid. 3. The locking code is tangled with code that starts and stops httpd, which is just incorrect, and very confusing. As a result, perf tests are skipped on Mac entirely. I'd like to remove the code, and if someone wants to revive the tests, a new correct solution should be found. Ossy suggested running these tests as a separate step, which makes sense to me, but would complicate error reporting on buildbot and EWS.