doc: Remove the description of lxc-kill in Japanese lxc-execute(1)

Update for commit 33ddfc2adef00e3571137ef60d20de328e32d299

Signed-off-by: KATOH Yasufumi <karma@jazz.email.ne.jp>
Acked-by: Stéphane Graber <stgraber@ubuntu.com>
Add Japanese lxc-usernsexec(1) and fix typo English lxc-usernsexec(1)

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