Use generate* from TestFramework

The changes in feature_rbf can be reviewed with
--color-moved=dimmed-zebra --color-moved-ws=ignore-all-space

test/functional/mempool_limit.py

@@ -32,7 +32,7 @@ class MempoolLimitTest(BitcoinTestFramework):
         assert_equal(self.nodes[0].getmempoolinfo()['mempoolminfee'], Decimal('0.00001000'))
 
         txids = []
-        utxos = create_confirmed_utxos(relayfee, self.nodes[0], 91)
+        utxos = create_confirmed_utxos(self, relayfee, self.nodes[0], 91)
 
         self.log.info('Create a mempool tx that will be evicted')
         us0 = utxos.pop()