Depth/stencil content defined is already tracked separately in the
ImageHelper.  This change exposes this tracking from RenderTargetVk.

Bug: b/167275320
Bug: angleproject:4836
Change-Id: Ie6520e7a4ab557eb233c60c6ab0d4a8f8f098bf6
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2462039
Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Ian Elliott <ianelliott@google.com>