Revert "parisc: Mark sched_clock unstable only if clocks are not syncronized"

This reverts commit d97180ad.

It triggers RCU stalls at boot with a 32-bit kernel.

Signed-off-by: Helge Deller <deller@gmx.de>
Noticed-by: John David Anglin <dave.anglin@bell.net>
Cc: stable@vger.kernel.org # v5.15+