RFR (trivial) 8198635: Remove unused safepoint message functions and ShowSafepointMsgs

[coleen.phillimore at oracle.com]

See bug for more info.
Tested with mach5 tier1 and

%java -XX:+ShowSafepointMsg -version
Java HotSpot(TM) 64-Bit Server VM warning: Ignoring option 
ShowSafepointMsgs; support was removed in 11.0

open webrev at http://cr.openjdk.java.net/~coleenp/8198635.01/webrev
bug link https://bugs.openjdk.java.net/browse/JDK-8198635

Thanks,
Coleen