bpo-31681: Make sure pkgutil.get_data closes files properly (#3875)

Also remove an obsolete note about
backward compat with old Pythons.
diff --git a/Lib/pkgutil.py b/Lib/pkgutil.py
index ce072ec..68ca72b 100644
--- a/Lib/pkgutil.py
+++ b/Lib/pkgutil.py
@@ -1,8 +1,5 @@
 """Utilities to support packages."""
 
-# NOTE: This module must remain compatible with Python 2.3, as it is shared
-# by setuptools for distribution with Python 2.3 and up.
-
 import os
 import sys
 import imp
@@ -252,7 +249,8 @@
         return mod
 
     def get_data(self, pathname):
-        return open(pathname, "rb").read()
+        with open(pathname, "rb") as file:
+            return file.read()
 
     def _reopen(self):
         if self.file and self.file.closed: