s4: server: Remove use of talloc_autofree_context as the parent of event_ctx.

s4: server: Remove use of talloc_autofree_context as the parent of event_ctx.

Use state->event_ctx as the parent of the initial imessaging context.

Now we control all exit paths, we can call TALLOC_FREE(state)
on all of them.

Signed-off-by: Jeremy Allison <jra@samba.org>
Reviewed-by: Volker Lendecke <vl@samba.org>