Revert "rtmutex: Handle the various new futex race conditions"

[ Upstream commit 9e0265c21af4d6388d47dcd5ce20f76ec3a2e468 ]

Drop the RT fixup, the futex code will be changed to avoid the need for
the workaround.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>