Use standard Abseil mutex
Use standard Abseil mutex

Previously, we used Abseil's "non-prod" mutex due to incompatibilities
with the standard mutex. Asylo can now use the standard mutex, so this
change switches our Abseil patch to do so.

PiperOrigin-RevId: 221538448

google/asylo,google/asylo,google/asylo,google/asylo,google/asylo,google/asylo