sshmem/verbs: So long / farewell / it's time to say goodnight

So long sshmem/verbs!  After many years of (mostly) faithful service,
it is time to remove the sshmem verbs component.  It has been fully
replaced by other components, such as the UCX PML and OFI MTL.

Signed-off-by: Jeff Squyres <jsquyres@cisco.com>

Author: jsquyres