The origin trial for WebAssembly Threads is over for quite some time,
WebAssembly Threads are enabled by default. The API can therefore be
removed now.

Bug: v8:11384
Change-Id: I3dd65ff63c1ed31d39a76e5aea08b950ef420f54
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2690598Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Commit-Queue: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#72766}