Now that we're using the helper everywhere, we can clean up the
vk::Image class and move the layout tracking into ImageHelper.

Bug: angleproject:2318
Change-Id: I9636835a2a3a76f181dac629bd4182bc5815cdee
Reviewed-on: https://chromium-review.googlesource.com/980774
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Frank Henigman <fjhenigman@chromium.org>