For unused variables reported by pyflakes, either remove the variable,

suppress the warning, or fix a bug (if the wrong variable was used).
refs #2450

Signed-off-by: Daira Hopwood <daira@jacaranda.org>

qa/rpc-tests/wallet_nullifiers.py

@@ -154,6 +154,7 @@ class WalletNullifiersTest (BitcoinTestFramework):
                 status = results[0]["status"]
                 assert_equal("success", status)
                 mytxid = results[0]["result"]["txid"]
+                [mytxid] # hush pyflakes
                 break
 
         self.sync_all()