watch: use chaintopology

Rather than polling for interesting bitcoin txs via importaddress, we use
the chain topology to register our interest directly.x 

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

daemon/lightningd.c

@@ -274,9 +274,6 @@ int main(int argc, char *argv[])
 	/* Set up node ID and private key. */
 	secrets_init(dstate);
 
-	/* Create timer to do watches. */
-	setup_watch_timer(dstate);
-
 	/* Initialize block topology. */
 	setup_topology(dstate);