Revert "[llvm][docs] commit phabricator patch"

This reverts commit ef4beb8b.

It also removes the prior note about needing to patch ``arcanist``.

This is patch is no longer necessary:
1. arcanist came out of hibernation and updated to support PHP 8.1.
   https://github.com/phacility/arcanist/commits/master
2. llvm/llvm-project is moving to github pull requests starting Sept 1
   (tomorrow).
   https://discourse.llvm.org/t/pull-request-migration-schedule/71595

Fixes: #64470

Reviewed By: MaskRay

Differential Revision: https://reviews.llvm.org/D159291