[graphite] Remove vertex buffer bind tracking logic from metal and vulkan.

* Tracking of currently bound buffers is now done (at a higher level) in DrawWriter.

* Removes now redundant tracking of currently bound buffers in Vulkan and Metal backends. (Dawn did not yet implement this feature, so there was nothing to remove.)


Change-Id: I25f399f115f69957844c3f02c160b4cabc2d0f80
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/991037
Commit-Queue: Thomas Smith <thomsmit@google.com>
Reviewed-by: Michael Ludwig <michaelludwig@google.com>
3 files changed