graphics/mesa-devel: drop userptr workaround after 2ad6d0d7f8fc
UNSYNCHRONIZED doesn't work on FreeBSD since drm-515-kmod.
https://github.com/torvalds/linux/commit/c6bcc0c2fdfd
This reverts commit 058e5ba0ff29ae64383b8392f23facad616be8c9.
PR: 244877