Use existing PME f ready event in PmeForceSenderGpu

Use existing PME f ready event in PmeForceSenderGpu

Instead of recording internally into the PME stream and sending that
event to the PP rank to sycn on from the separate PME rank, use the
already existing event recorded in PME.
This also eliminates the unnecessary use of multiple events, one for
each PP rank.

Refs #2891 #2915