Revert "Add tests for coverage mapping generation."

I reverted one of the added tests from r215261 in r215274, since it
was failing on quite a few bots. It looks like this wasn't sufficient,
as we're still getting failures on windows, like the following:

    http://bb.pgr.jp/builders/ninja-x64-msvc-RA-centos6/builds/5378

I'm reverting this entire commit so the bots aren't blocked on these
failures.

This reverts commit r215261.