contrib: Use text=True in subprocess over manual encoding handling

All touched Python scripts already assume and require UTF8, so manually
specifying encoding or decoding for functions in the subprocess module
is redundant to just using text=True, which exists since Python 3.7

test/lint/lint-submodule.py

@@ -1,6 +1,6 @@
 #!/usr/bin/env python3
 #
-# Copyright (c) 2022 The Bitcoin Core developers
+# Copyright (c) 2022-present The Bitcoin Core developers
 # Distributed under the MIT software license, see the accompanying
 # file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
@@ -13,7 +13,7 @@ import sys
 
 def main():
     submodules_list = subprocess.check_output(['git', 'submodule', 'status', '--recursive'],
-                                                text = True, encoding = 'utf8').rstrip('\n')
+                                                text = True).rstrip('\n')
     if submodules_list:
         print("These submodules were found, delete them:\n", submodules_list)
         sys.exit(1)