common, osd: Remove unused implementation of mClockPriorityQueue

common, osd: Remove unused implementation of mClockPriorityQueue

mClockPriorityQueue (mClockQueue class) is an older mClock implementation
of the OpQueue abstraction. This was replaced by a simpler implementation
of the OpScheduler abstraction as part of
https://github.com/ceph/ceph/pull/30650.

The simpler implementation of mClockScheduler is being currently used.
This commit removes the unused src/common/mClockPriorityQueue.h along
with the associated unit test file: test_mclock_priority_queue.cc.

Other miscellaneous changes,
 - Remove the cmake references to the unit test file
 - Remove the inclusion of the header file in mClockScheduler.h

Signed-off-by: Sridhar Seshasayee <sseshasa@redhat.com>