[floc] Use sorting-lsh by default. Remove base::Feature and clean up …

…tests.

Bug: 1190992
Change-Id: Ibc8e206053e604b09a781352ad6e311dceff3528
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2779431
Reviewed-by: Josh Karlin <jkarlin@chromium.org>
Commit-Queue: Yao Xiao <yaoxia@chromium.org>
Cr-Commit-Position: refs/heads/master@{#868285}