migration/rdma: Plug memory leaks in qemu_rdma_registration_stop()

migration/rdma: Plug memory leaks in qemu_rdma_registration_stop()

qemu_rdma_registration_stop() uses the ERROR() macro to create, report
to stderr, and store an Error object.  The stored Error object is
never used, and its memory is leaked.

Even where ERROR() doesn't leak, it is ill-advised.  The whole point
of passing an Error to the caller is letting the caller handle the
error.  Error handling may report to stderr, to somewhere else, or not
at all.  Also reporting in the callee mixes up concerns that should be
kept separate.  Since I don't know what reporting to stderr is
supposed to accomplish, I'm not touching it.

Commit 2a1bc8bde7 "migration/rdma: rdma_accept_incoming_migration fix
error handling" plugged the same leak in
rdma_accept_incoming_migration().

Plug the memory leak the same way: keep the report part, delete the
store part.

The report part uses fprintf().  If it's truly an error, it should use
error_report() instead.  But I don't know, so I leave it alone, just
like commit 2a1bc8bde7 did.

Fixes: 2da776db4846eadcb808598a5d3484d149773c05
Cc: Dr. David Alan Gilbert <dgilbert@redhat.com>
Cc: Juan Quintela <quintela@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20200630090351.1247703-27-armbru@redhat.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>