test: Fix wallet_balance intermittent issue

Fix it by removing a duplicate balance check on the same node.

test/functional/wallet_balance.py

@@ -266,7 +266,6 @@ class WalletTest(BitcoinTestFramework):
         self.nodes[1].invalidateblock(block_reorg)
         assert_equal(self.nodes[0].getbalance(minconf=0), 0)  # wallet txs not in the mempool are untrusted
         self.generatetoaddress(self.nodes[0], 1, ADDRESS_WATCHONLY, sync_fun=self.no_op)
-        assert_equal(self.nodes[0].getbalance(minconf=0), 0)  # wallet txs not in the mempool are untrusted
 
         # Now confirm tx_orig
         self.restart_node(1, ['-persistmempool=0'])