RFR: 8233280: Remove GCLockerInvokesConcurrent

[Kim Barrett]

Please review this change to obsolete the GCLockerInvokesConcurrent
product option, as a step toward removal.  Normally removal of a
product option involves a 3-step process of deprecate, obsolete, and
remove.  In this case, for reasons discussed in the CR and the
associated CSR, we propose to skip the deprecation step and go
straight to obsolete.

CR:
https://bugs.openjdk.java.net/browse/JDK-8233280

Webrev:
https://cr.openjdk.java.net/~kbarrett/8233280/open.00/

Testing:
Local (linux-x64) build and hotspot:tier1.

Searched the entire source tree (including Oracle's closed part) for
references, finding none except the new entry in the special_jvm_flags
table.

Verified this option is not mentioned in the GC Tuning Guide.