bulk-memory shipped in V8 v7.5, hence the feature flag can be removed
now. This saves some binary size and a few dynamic checks for the flag.

R=ahaas@chromium.org

Bug: v8:11074
Change-Id: Ia73622637939f2192940fdd6909520786ed27286
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2622913Reviewed-by: Andreas Haas <ahaas@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#72045}