Remove ProtectionDomainSet_lock

The following test timed out in the JDK16 CI:

vmTestbase/vm/mlvm/mixed/stress/java/findDeadlock/TestDescription.java

Here's a snippet from the log file:

#section:main
----------messages:(6/320)----------
command: main -Xlog:gc,safepoint vm.mlvm.mixed.stress.java.findDeadlock.INDIFY_Test
reason: User specified action: run main/othervm -Xlog:gc,safepoint vm.mlvm.mixed.stress.java.findDeadlock.INDIFY_Test
Mode: othervm [/othervm specified]
Timeout information:
--- Timeout information end.
elapsed time (seconds): 488.254
----------configuration:(0/0)----------
----------System.out:(526/79192)----------
[0.015s][info][gc] Using G1
[0.060s][info][safepoint] Safepoint "Verify", Time since last: 1137449 ns, Reaching safepoint: 37799 ns, At safepoint: 4362752 ns, Total: 4400551 ns
[0.064s][info][safepoint] Safepoint "Verify", Time since last: 78439 ns, Reaching safepoint: 41718 ns, At safepoint: 3998675 ns, Total: 4040393 ns
[0.070s][info][safepoint] Safepoint "Verify", Time since last: 1342272 ns, Reaching safepoint: 29389 ns, At safepoint: 4484275 ns, Total: 4513664 ns
[0.075s][info][safepoint] Safepoint "Verify", Time since last: 78798 ns, Reaching safepoint: 26330 ns, At safepoint: 4525471 ns, Total: 4551801 ns

<snip>

[480.261s][info][safepoint] Safepoint "FindDeadlocks", Time since last: 46709 ns, Reaching safepoint: 344201 ns, At safepoint: 1641097 ns, Total: 1985298 ns
[480.264s][info][safepoint] Safepoint "FindDeadlocks", Time since last: 64298 ns, Reaching safepoint: 318325 ns, At safepoint: 2399781 ns, Total: 2718106 ns
[480.269s][info][safepoint] Safepoint "FindDeadlocks", Time since last: 74795 ns, Reaching safepoint: 3356152 ns, At safepoint: 2018886 ns, Total: 5375038 ns
[480.271s][info][safepoint] Safepoint "FindDeadlocks", Time since last: 1107723 ns, Reaching safepoint: 375736 ns, At safepoint: 651935 ns, Total: 1027671 ns
### TRACE 1: TEST PASSED
----------System.err:(0/0)----------
----------rerun:(41/8355)*----------