We potentially emitted the same gap move multiple times to satisfy slot
constraint of live ranges defined by a constant. Avoid this by keeping
track of already spilled ranges for a given instruction.

This is not expected to cause any regression because this case is rare.
If it does, a better approach to save allocations would be to re-use the
same vector by storing it somewhere that survives the function calls,
e.g. in the ConstraintBuilder.

Drive-by: Remove unused functions.

R=sigurds@chromium.org
CC=nicohartmann@chromium.org

Bug: chromium:1204748
Change-Id: I75a838a8b27775ecdeddb4c60cf72c56d5f1c2a4
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2871462Reviewed-by: Sigurd Schneider <sigurds@chromium.org>
Commit-Queue: Thibaud Michaud <thibaudm@chromium.org>
Cr-Commit-Position: refs/heads/master@{#74375}