RFR 8235766: SafepointSynchronize::_end_of_last_safepoint is unused

[Harold Seigel]

Hi,

Please review this trivial JDK-15 fix to remove 
SafepointSynchronize::_end_of_last_safepoint.

Open Webrev: http://cr.openjdk.java.net/~hseigel/bug_8235766/webrev/

JBS Bug: https://bugs.openjdk.java.net/browse/JDK-8235766

The fix was regression tested by running Mach5 tiers 1 and 2 tests and 
builds on Linux-x64, Solaris, Windows, and Mac OS X.

Thanks, Harold