Many of our tests rely on extensions and ES3 support. Until we
have the ability to switch between Renderers for specific tests,
the D3D11 Renderer should enable many failing tests to pass.

Also fix a double-delete crash in the test cleanup routine.

BUG=angle:702

Change-Id: I5e615ca1a35bd109d9f7bcbb5fa90b88e09157bd
Reviewed-on: https://chromium-review.googlesource.com/209102Reviewed-by: Geoff Lang <geofflang@chromium.org>
Tested-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Zhenyao Mo <zmo@chromium.org>