clientIF: Remove unused _memLock

_memLock was used by memTestAndCommit(), which was removed in 6fcfb09456
on May 2011.

Change-Id: I3ef120e4363dae9c9cf06d31128b715392f552b8
Signed-off-by: Nir Soffer <nsoffer@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/26206
Reviewed-by: Dan Kenigsberg <danken@redhat.com>
Tested-by: Dan Kenigsberg <danken@redhat.com>