Refactor: tools: Drop gratuitious pcmk_find_node() for cmd_digests

If options.host_uname != NULL, then we already got the node earlier in
main() or exited with an error.

And in fact options.host_uname must be non-NULL, because
is_node_required() returns true for cmd_digests.

Signed-off-by: Reid Wahl <nrwahl@protonmail.com>