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. (Or if we didn't get the node because
scheduler is NULL, then we would segfault here.)

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>