m4: remove all configury related to libibverbs

Now that all components that use libibverbs are gone, remove
OPAL_CHECK_VERBS and the confusingly-named OPAL_CHECK_OPENFABRICS
(which really just checked for verbs things -- not all the possible
OpenFabrics APIs/libraries).

The only code left in Open MPI that calls verbs is hwloc -- and that's
just the APIs that takes an IBV device and returns topological
information about it.  Since nothing in the Open MPI code base uses
the "ibv_*" API any more, we have no need for this hwloc functionality
so we'll even remove the --with-verbs configure options.

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

Author: jsquyres