RFR (S) 8223585: vmTestbase/runtime/pcl/* get SEGV in MetadataOnStackClosure::do_metadata(Metadata*)+0x0

[coleen.phillimore at oracle.com]

Summary: adjust old method table by only one thread.

Entries were removed from the redefinition old method table by G1 by 
multiple threads at a safepoint, so didn't take the CodeCache_lock. 
Moved the removal to nmethod->flush().  The bug is confidential because 
there's a confidential comment not marked confidential but we'll open it 
up once that's fixed.

Passed redefinition tests in repository with "VM_OPTIONS=-Xcomp 
-XX:TieredStopAtLevel=1", including the PCL tests that in the oracle 
closed repo.

Also ran hs-tier1-3.

open webrev at http://cr.openjdk.java.net/~coleenp/2019/8223585.01/webrev
bug link https://bugs.openjdk.java.net/browse/JDK-8223585

Thanks,
Coleen