RFR: 8185746: Remove Mutex destructor assertion

[Kim Barrett]

Please review this small change to improve the debugging experience
when a mutex is destroyed in a bad state.

I've removed the assert in ~Mutex, which was making the same checks as
in ~Monitor, but providing much less information.

Also, the ~Monitor assert now (carefully) includes the name in the
error message, as that may also be very helpful information.

CR:
https://bugs.openjdk.java.net/browse/JDK-8185746

Webrev:
http://cr.openjdk.java.net/~kbarrett/8185746/hotspot.00/

Testing:
Destroyed a locked mutex and looked at the assert message.