CMS was using some of the VM ops more complicated features.
Now that CMS is removed we no longer have any use for them.
Other GCs handle this work without using complicated VM op features
and do not need this functionality, which is a better approach.

This means all VM ops can be stack allocated and synchronous.
We thus remove concurrent (non-safepoint heap allocated) and
asynchronous (safepoint heap allocated) ops.

There are some future features which could utilize concurrent handshake operations.
These would mainly be single Java thread targeted handshakes and thus would not use a VM op.
That assumes we have Thread->JavaThread handshake support.
Currently we always do Thread->VM Thread (via VM op)->JavaThread.