libEGL should use libGLESv2 for EGL implementation,
to prevent libANGLE global variables being duplicated.

BUG=angleproject:1660

Change-Id: I84c1e22fcce8f4a21acfb1fcde0c84ebd77204f8
Reviewed-on: https://chromium-review.googlesource.com/422574Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Yuly Novikov <ynovikov@chromium.org>