RFR: 8078021: SATB apply_closure_to_completed_buffer should have closure argument

[Kim Barrett]

Please review this simplification to SATB buffer processing.

SATBMarkQueueSet::apply_closure_to_completed_buffer() presently takes
a worker_id index. It uses that to look up the closure associated with
the worker by a preceding call to set_closure.

There is only one caller of this apply function,
CMTask::drain_satb_buffers. It creates the desired closure, associates
the closure with its worker id, calls
apply_closure_to_completed_buffer, and clears the associated buffer.

We're changing the apply function to now take the closure directly, as
an argument, replacing the worker_id argument that is now unused. We
then eliminate set_closure and the supporting infrastructure, which
are no longer used.

CR:
https://bugs.openjdk.java.net/browse/JDK-8078021

Webrev:
http://cr.openjdk.java.net/~kbarrett/8078021/webrev.00/

Testing:
JPRT