Those methods are used by VMA. However VMA can get those methods
by itself, if null function pointers are provided for creating
the VMA. But it will cause problem, when ANGLE & Chromium are
sharing one VMA implementation, since the VMA implementation
in chromium will be built with VMA_STATIC_VULKAN_FUNCTIONS=0 &
VMA_DYNAMIC_VULKAN_FUNCTIONS=0.

Bug: chromium:1170339
Change-Id: I5bf435698e4e361bfa7a6afce84390ccc4355b53
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2655795Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>