RFR 8196535: Remove support for pre-Java 6 non-JVM-wide file locking

[Brian Burkhalter]

https://bugs.openjdk.java.net/browse/JDK-8196535
http://cr.openjdk.java.net/~bpb/8196535/webrev.00/

This patch would remove support for the sun.nio.ch.disableSystemWideOverlappingFileLockCheck system property introduced in Java 6 to allow enabling pre-Java 6 behavior of checking for overlapping FileLocks opened on a FileChannel.

Please note that this patch follows in sequence the patch proposed in [1] which still needs to pass review.

Thanks,

Brian

[1] http://mail.openjdk.java.net/pipermail/nio-dev/2018-February/004667.html