Remove and replace compat.UnicodeMixin

Author: Harmon758

git/compat.py

@@ -76,17 +76,3 @@ def __new__(cls, name, nbases, d):
                 d['__metaclass__'] = meta
             return meta(name, bases, d)
     return metaclass(meta.__name__ + 'Helper', None, {})
-
-
-## From https://docs.python.org/3.3/howto/pyporting.html
-class UnicodeMixin(object):
-
-    """Mixin class to handle defining the proper __str__/__unicode__
-    methods in Python 2 or 3."""
-
-    if PY3:
-        def __str__(self):
-            return self.__unicode__()
-    else:  # Python 2
-        def __str__(self):
-            return self.__unicode__().encode(defenc)

git/exc.py

@@ -6,7 +6,7 @@
 """ Module containing all exceptions thrown throughout the git package, """
 
 from gitdb.exc import *     # NOQA @UnusedWildImport skipcq: PYL-W0401, PYL-W0614
-from git.compat import UnicodeMixin, safe_decode, string_types
+from git.compat import safe_decode, string_types
 
 
 class GitError(Exception):
@@ -25,7 +25,7 @@ class NoSuchPathError(GitError, OSError):
     """ Thrown if a path could not be access by the system. """
 
 
-class CommandError(UnicodeMixin, GitError):
+class CommandError(GitError):
     """Base class for exceptions thrown at every stage of `Popen()` execution.
 
     :param command:
@@ -58,7 +58,7 @@ def __init__(self, command, status=None, stderr=None, stdout=None):
         self.stdout = stdout and u"\n  stdout: '%s'" % safe_decode(stdout) or ''
         self.stderr = stderr and u"\n  stderr: '%s'" % safe_decode(stderr) or ''
 
-    def __unicode__(self):
+    def __str__(self):
         return (self._msg + "\n  cmdline: %s%s%s") % (
             self._cmd, self._cause, self._cmdline, self.stdout, self.stderr)