Bug: angleproject:2482

Moving to HEAD of master as of 4/18/18.
Disable workaround to copy reg.py in BUILD.gn.
Re-enable ANGLE Vulkan build.

Change-Id: I62d79f532bf8fed40872ee9c175caa4b51c2dd25
Reviewed-on: https://chromium-review.googlesource.com/1016683Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>