doc: Remove unneeded "SEE ALSO" part in lxc-ls(1)

The old version of lxc-ls is the wrapper of ls(1). But now it is
python script, so "see also ls(1)" is not needed.

Signed-off-by: KATOH Yasufumi <karma@jazz.email.ne.jp>
Acked-by: Stéphane Graber <stgraber@ubuntu.com>