test: refactor: replace unnecessary BytesIO uses

Rather than needing to create intermediate stream variables, we can use
helper functions like `tx_from_hex` instead or access the result
directly, leading both to increased readability and less code.

test/functional/feature_taproot.py

@@ -19,6 +19,7 @@ from test_framework.messages import (
     CTxInWitness,
     CTxOut,
     SEQUENCE_FINAL,
+    tx_from_hex,
 )
 from test_framework.script import (
     ANNEX_TAG,
@@ -109,7 +110,6 @@ from test_framework.address import (
     program_to_witness,
 )
 from collections import OrderedDict, namedtuple
-from io import BytesIO
 import json
 import hashlib
 import os
@@ -1386,8 +1386,7 @@ class TaprootTest(BitcoinTestFramework):
             # Add change
             fund_tx.vout.append(CTxOut(balance - 10000, random.choice(host_spks)))
             # Ask the wallet to sign
-            ss = BytesIO(bytes.fromhex(node.signrawtransactionwithwallet(fund_tx.serialize().hex())["hex"]))
-            fund_tx.deserialize(ss)
+            fund_tx = tx_from_hex(node.signrawtransactionwithwallet(fund_tx.serialize().hex())["hex"])
             # Construct UTXOData entries
             fund_tx.rehash()
             for i in range(count_this_tx):