[11u] RFR: 8222518: Remove unnecessary caching of Parker object in java.lang.Thread

[Hohensee, Paul]

Please review this small code deletion and footprint reduction backport.

JBS: https://bugs.openjdk.java.net/browse/JDK-8222518
Original patch: http://hg.openjdk.java.net/jdk/jdk/rev/9ebb614d293d
Webrev: http://cr.openjdk.java.net/~phh/8222518/webrev.11u.00/

The backport is not clean because (1) javaClasses.cpp needed a copyright date update to 2019 and the original 3rd hunk that deletes park_event() and set_park_event() contained slightly different code that does not check for non-existent Thread fields, and (2) unsafe.cpp needed a copyright update to 2019.

Thanks,
Paul