Use system Vulkan headers except when no building with vulkan support

We now will always use the system vulkan.h files whenever we are building
with vulkan. With non vulkan builds we use our checked in header to so
that we can get the needed symbols for compiling.

Bug: skia:
Change-Id: I352a3e007b33c575cefcfd6752db0b3b12b86a16
Reviewed-on: https://skia-review.googlesource.com/14270
Commit-Queue: Greg Daniel <egdaniel@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
5 files changed