Please review this change which obsoletes the UseMembar flag and removes the code that then becomes unreachable/dead.

bug: https://bugs.openjdk.java.net/browse/JDK-8213436

webrev: http://cr.openjdk.java.net/~mikael/webrevs/8213436/webrev.00/open/webrev/

* Background (from jbs)

The UseMembar flag was deprecated in JDK 10, and is default true/enabled on all platforms since that same release. It should be obsoleted and the then dead serialization page functionality it controls should be removed.

* Testing

tier1. If anybody wants to take it for a spin on aarch64/ppc/s390/x86_32 that wouldn’t hurt.

(Unrelated to this change: It would be really nice to clean up some of the (mostly) duplicated code in the os/signal handling area...)

Cheers,

Mikael