test: refactor: remove hex_str_to_bytes helper

Use the built-in class method bytes.fromhex() instead,
which is available since Python 3.0.

test/functional/test_framework/wallet.py

@@ -27,7 +27,6 @@ from test_framework.script import (
 )
 from test_framework.util import (
     assert_equal,
-    hex_str_to_bytes,
     satoshi_round,
 )
 
@@ -73,7 +72,7 @@ class MiniWallet:
             self._scriptPubKey = bytes(CScript([pub_key.get_bytes(), OP_CHECKSIG]))
         elif mode == MiniWalletMode.ADDRESS_OP_TRUE:
             self._address = ADDRESS_BCRT1_P2WSH_OP_TRUE
-            self._scriptPubKey = hex_str_to_bytes(self._test_node.validateaddress(self._address)['scriptPubKey'])
+            self._scriptPubKey = bytes.fromhex(self._test_node.validateaddress(self._address)['scriptPubKey'])
 
     def scan_blocks(self, *, start=1, num):
         """Scan the blocks for self._address outputs and add them to self._utxos"""