Accidentally disabled in 26581113, which intended to disable tests
requiring GL_ANGLE_framebuffer_blit, but also disabled glBlitFramebuffer
tests.  glBlitFramebuffer is core, but was conditioned to
EXT_framebuffer_blit.

Bug: angleproject:2773
Change-Id: I0468af8874dc8676a4eb6214b111c08aadc0e2fc
Reviewed-on: https://chromium-review.googlesource.com/1186543Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>