contrib: Remove confusing and redundant encoding from IO

The encoding arg is confusing, because it is not applied consistently
for all IO.

Also, it is useless, as the majority of files are ASCII encoded, which
are fine to encode and decode with any mode.

Moreover, UTF-8 is already required for most scripts to work properly,
so setting the encoding twice is redundant.

So remove the encoding from most IO. It would be fine to remove from all
IO, however I kept it for two files:

* contrib/asmap/asmap-tool.py: This specifically looks for utf-8
  encoding errors, so it makes sense to sepecify the utf-8 encoding
  explicitly.
* test/functional/test_framework/test_node.py: Reading the debug log in
  text mode specifically counts the utf-8 characters (not bytes), so it
  makes sense to specify the utf-8 encoding explicitly.

test/lint/lint-includes.py

@@ -40,13 +40,13 @@ EXPECTED_BOOST_INCLUDES = [
 
 
 def get_toplevel():
-    return check_output(["git", "rev-parse", "--show-toplevel"], text=True, encoding="utf8").rstrip("\n")
+    return check_output(["git", "rev-parse", "--show-toplevel"], text=True).rstrip("\n")
 
 
 def list_files_by_suffix(suffixes):
     exclude_args = [":(exclude)" + dir for dir in EXCLUDED_DIRS]
 
-    files_list = check_output(["git", "ls-files", "src"] + exclude_args, text=True, encoding="utf8").splitlines()
+    files_list = check_output(["git", "ls-files", "src"] + exclude_args, text=True).splitlines()
 
     return [file for file in files_list if file.endswith(suffixes)]
 
@@ -68,7 +68,7 @@ def find_included_cpps():
     included_cpps = list()
 
     try:
-        included_cpps = check_output(["git", "grep", "-E", r"^#include [<\"][^>\"]+\.cpp[>\"]", "--", "*.cpp", "*.h"], text=True, encoding="utf8").splitlines()
+        included_cpps = check_output(["git", "grep", "-E", r"^#include [<\"][^>\"]+\.cpp[>\"]", "--", "*.cpp", "*.h"], text=True).splitlines()
     except CalledProcessError as e:
         if e.returncode > 1:
             raise e
@@ -82,7 +82,7 @@ def find_extra_boosts():
     exclusion_set = set()
 
     try:
-        included_boosts = check_output(["git", "grep", "-E", r"^#include <boost/", "--", "*.cpp", "*.h"], text=True, encoding="utf8").splitlines()
+        included_boosts = check_output(["git", "grep", "-E", r"^#include <boost/", "--", "*.cpp", "*.h"], text=True).splitlines()
     except CalledProcessError as e:
         if e.returncode > 1:
             raise e
@@ -105,7 +105,7 @@ def find_quote_syntax_inclusions():
     quote_syntax_inclusions = list()
 
     try:
-        quote_syntax_inclusions = check_output(["git", "grep", r"^#include \"", "--", "*.cpp", "*.h"] + exclude_args, text=True, encoding="utf8").splitlines()
+        quote_syntax_inclusions = check_output(["git", "grep", r"^#include \"", "--", "*.cpp", "*.h"] + exclude_args, text=True).splitlines()
     except CalledProcessError as e:
         if e.returncode > 1:
             raise e
@@ -120,7 +120,7 @@ def main():
 
     # Check for duplicate includes
     for filename in list_files_by_suffix((".cpp", ".h")):
-        with open(filename, "r", encoding="utf8") as file:
+        with open(filename, "r") as file:
             include_list = [line.rstrip("\n") for line in file if re.match(r"^#include", line)]
 
         duplicates = find_duplicate_includes(include_list)
@@ -148,13 +148,13 @@ def main():
     if extra_boosts:
         for boost in extra_boosts:
             print(f"A new Boost dependency in the form of \"{boost}\" appears to have been introduced:")
-            print(check_output(["git", "grep", boost, "--", "*.cpp", "*.h"], text=True, encoding="utf8"))
+            print(check_output(["git", "grep", boost, "--", "*.cpp", "*.h"], text=True))
         exit_code = 1
 
     # Check if Boost dependencies are no longer used
     for expected_boost in EXPECTED_BOOST_INCLUDES:
         try:
-            check_output(["git", "grep", "-q", r"^#include <%s>" % expected_boost, "--", "*.cpp", "*.h"], text=True, encoding="utf8")
+            check_output(["git", "grep", "-q", r"^#include <%s>" % expected_boost, "--", "*.cpp", "*.h"], text=True)
         except CalledProcessError as e:
             if e.returncode > 1:
                 raise e