Deleted LayoutTests/webgl folder.

Work is ongoing to run these tests in a different harness on GPU bots, and there are no resources available to deal with any flakiness that arises from running these tests with the Mesa renderer on the Blink bots.

Removed associated TestExpectations entry.

Ran layout tests on Linux to verify. Not uploading this CL to the review tool as it's too large.

BUG=174268
TBR=ojan@chromium.org,dpranke@chromium.org

git-svn-id: svn://svn.chromium.org/blink/trunk@155195 bbb929c8-8fbe-4397-9dbb-9b2b20218538