Disconnect the OPENSTACK target from the CLOUDWARE list.

This was reported to not work as expected, and feedback
following the report was never received.  In addition, we
do not publish these anywhere publicly.

The configuration file is not (yet) removed, in hopes that
the remaining details on the original issues can be resolved,
and we can publish the resulting images in the future.

Sponsored by:	The FreeBSD Foundation

release/Makefile.vm

@@ -17,7 +17,6 @@ RAW_DESC=	Unformatted raw disk image
 
 CLOUDWARE?=	EC2 \
 		GCE \
-		OPENSTACK \
 		VAGRANT-VIRTUALBOX \
 		VAGRANT-VMWARE
 AZURE_FORMAT=	vhdf