This CL adds lint errors for unused Torque macros. To prevent lots of
noisy warnings, the check is rather narrow. Macros declared as "extern"
or marked with "@export" are ignored. Also macros starting with "Convert",
"Cast" or "FromConstexpr" are not checked.

Drive-by: Removing some unused macros.

Bug: v8:7793
Change-Id: Ie0d2e445f8882a9b0ebbda45876b342abf341248
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1645312
Commit-Queue: Simon Zünd <szuend@chromium.org>
Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#62092}