[rpc] Remove signrawtransaction warning

signrawtransaction was deprecated in 0.17 and removed in 0.18. A warning
was left in place to tell users to migrate to using
signrawtransactionswithwallet or signrawtransactionwithkey. Remove the
warning now that it's been two releases since the method was removed.

test/functional/rpc_signrawtransaction.py

@@ -15,7 +15,6 @@ class SignRawTransactionsTest(BitcoinTestFramework):
     def set_test_params(self):
         self.setup_clean_chain = True
         self.num_nodes = 2
-        self.extra_args = [["-deprecatedrpc=signrawtransaction"], []]
 
     def skip_test_if_missing_module(self):
         self.skip_if_no_wallet()