Remove CanvasResource::IsOverlayCandidate

All implementation use usage().Has(SCANOUT) for the shared image that
is returned from GetClientSharedImage().

The only call-site is when we call TransferableResource::Make, and it
interally would get it from client shared image if not overriden.

https://source.chromium.org/chromium/chromium/src/+/main:components/viz/common/resources/transferable_resource.cc;drc=f568e8592b3f5477be70e22e5891161b06c6911b;l=76

Bug: 390568190
Change-Id: Ic920573c8e45424dd9e3e4f73946304269895471
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6187582
Reviewed-by: Colin Blundell <blundell@chromium.org>
Commit-Queue: Vasiliy Telezhnikov <vasilyt@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1409626}