ctdb-daemon: Drop use of strdup(3) and free(3) when releasing IP

ctdb-daemon: Drop use of strdup(3) and free(3) when releasing IP

If anything should be used here it should be talloc functions.
However, this is a remnant from when ctdb_sys_find_ifname() was used
here and, for some reason, it used strdup(3).

In this case the interface string doesn't actually need to be copied.
The only use of it is when ctdb_event_script_callback_v() uses it with
the format string in a call to talloc_vasprintf().  In the same
context the IP address isn't copied.

Signed-off-by: Martin Schwenke <martin@meltin.net>
Reviewed-by: Amitay Isaacs <amitay@gmail.com>