libplugin: mark the cmd notleak() whenever command_still_pending() called.

This is what we do in lightningd, which makes memleak much more forgiving:
you can hang temporaries off cmd without getting reports of leaks (also
when send_outreq called).

We remove all the notleak() calls in plugins which worked around this!
And avoid multiple notleak labels, since both send_outreq() and
command_still_pending() can be called multiple times.

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

plugins/bcli.c

@@ -782,9 +782,6 @@ static struct command_result *sendrawtransaction(struct command *cmd,
 	} else
 		highfeesarg = NULL;
 
-	/* Keep memleak happy! */
-	tal_free(allowhighfees);
-
 	start_bitcoin_cli(NULL, cmd, process_sendrawtransaction, true,
 			  BITCOIND_HIGH_PRIO, NULL,
 			  "sendrawtransaction",