Default --lookup-extents to no again

The default for --lookup-extents was set to "no" in
e1c8950b2e09fb3ac810a5f48b581e4b350c7ef9, but this regressed to "yes" in
1b77385f1ec28a145e6a2305561d149a7e1eb1e1.  Set this back to "no" to match
the information in duperemove.8

Signed-off-by: Matt Robinson <git@nerdoftheherd.com>