Don't redefine VMA_IMPLEMENTATION in build files and source VMA_IMPLEMENTATION is defined in the build files, it doesn't need to be redefined in vk_mem_alloc_wrapper.cpp. BUG=angleproject:2162 Change-Id: Ie4eceedd2dd3051f8431c7c8c86403250e93f98b Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2154538 Commit-Queue: Geoff Lang <geofflang@chromium.org> Reviewed-by: Jamie Madill <jmadill@chromium.org>