From angle_vulkan build target,
so that everyone including Vulkan Headers
would get them for the right platform.

Also remove obsolete defines.

Bug: angleproject:3279
Change-Id: I4bbbeb72acfbf0dd22a1d6a13bd9df7ddaec84dd
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1530029Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Tobin Ehlis <tobine@google.com>
Commit-Queue: Yuly Novikov <ynovikov@chromium.org>