RFR (T) 8225628: Remove unused Thread::muxAcquireW function

[coleen.phillimore at oracle.com]

I didn't find any historical use of this function.  It looks like a copy 
of muxAcquire where a different ParkEvent could be passed in or 
allocated for the park operation.

open webrev at http://cr.openjdk.java.net/~coleenp/2019/8225628.01/webrev
bug link https://bugs.openjdk.java.net/browse/JDK-8225628

Ran tier1 testing on all Oracle platforms.

Thanks,
Coleen