tweak how we avoid rewriting vulkan includes

This may be splitting hairs, but it occurred to me that this
might be a clearer way of expressing what we're trying to do,
avoiding treating include/third_party/vulkan as our own.

Change-Id: I2bb3c2da5b2294cc219d3a3745a6b52dd09ec21d
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/229801
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
1 file changed