RFR (XS) 8235273: nmethodLocker not needed for COMPILED_METHOD_UNLOAD events

[coleen.phillimore at oracle.com]

Summary: remove unnecessary nmethodLocker

See bug for more details.  Tested with tier2-8.

open webrev at http://cr.openjdk.java.net/~coleenp/2019/8235273.01/webrev
bug link https://bugs.openjdk.java.net/browse/JDK-8235273

(Note, this has a trivial merge with the change for JDK-8212160).

Thanks,
Coleen