common/cmdparse: no need to use (and leak to) the heap

Signed-off-by: Sage Weil <sage@inktank.com>
Reviewed-by: Dan Mick <dan.mick@inktank.com>
common/admin_socket: fix leak of new m_getdescs_hook

Signed-off-by: Sage Weil <sage@inktank.com>