We now we detect feedback loops by tracking the Framebuffers that the
Texture is bound to. We still have the old tracking method that counts
sampler and image bindings in the code as well.

This CL removes the old front-end tracking for feedback loops. It's no
longer used by any back-ends. This removal should reduce CPU overhead
around Texture and Program binding changes. Reverts the image binding
tracking to the simpler scheme that tracks if a Texture has ever been
bound as an Image. This should practically have little or no perf
effect and we can reinstate some simpler tracking in the future if
required.

Bug: angleproject:4500
Bug: angleproject:4959
Change-Id: Idc625d6e4c519919f97a4dc72dd9c35d262706fb
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2363210
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Tobin Ehlis <tobine@google.com>
Reviewed-by: Courtney Goeltzenleuchter <courtneygo@google.com>