Remove unnecessary write barrier

At the end of registerSignalHandlerWithOS, a write barrier is issued
before updating signalsWithHandlers. According to the comment, the write
barrier is required since registerHandlerMonitor isn't acquired.

registerSignalHandlerWithOS is invoked from:
1) registerMasterHandlers
2) omrsig_register_os_handler [registerHandlerMonitor acquired]

registerMasterHandlers is invoked from:
1) omrsig_protect [registerHandlerMonitor acquired]
2) omrsig_set_async_signal_handler [registerHandlerMonitor acquired]
3) omrsig_set_single_async_signal_handler [registerHandlerMonitor
acquired]

I have confirmed that registerHandlerMonitor is acquired for every call
to registerSignalHandlerWithOS. So, the write barrier is no longer
needed.

Signed-off-by: Babneet Singh <sbabneet@ca.ibm.com>

port/unix/omrsignal.c

@@ -1250,9 +1250,6 @@ registerSignalHandlerWithOS(OMRPortLibrary *portLibrary, uint32_t portLibrarySig
 		}
 	}
 
-	/* CMVC 96193 signalsWithHandlers is checked without acquiring the registerHandlerMonitor */
-	issueWriteBarrier();
-
 	/* we've successfully registered the handler for this, record it! */
 	signalsWithHandlers |= portLibrarySignalNo;