NMT: Remove VM.native_memory shutdown jcmd command option

NMT shutdown functionality is a remnant of old implementation, which could consume excessive amount of memory, therefore, it needed capability to shut it self down to ensure health of JVM. This is no longer a case for new implementation.

NMT shutdown can be requested via Jcmd. However, it is rare used.

We should deprecate for shutdown Jcmd command for removing NMT shutdown functionality in the future.