remove self._context

It's not necessary, since `GitConfig` object holds `git`.

Signed-off-by: Nanda Lopes <nandalopes@gmail.com>
(cherry picked from commit 22921eb)
Signed-off-by: David Aguilar <davvid@gmail.com>

cola/gitcfg.py

@@ -124,7 +124,6 @@ def __init__(self, context):
         self._cache_key = None
         self._configs = []
         self._config_files = {}
-        self._context = context
         self._attr_cache = {}
         self._find_config_files()
 
@@ -213,7 +212,7 @@ def read_config(self, path):
             return self._read_config_file(path)
 
         dest = {}
-        if version.check_git(self._context, 'config-includes'):
+        if version.check_git(self, 'config-includes'):
             args = ('--null', '--file', path, '--list', '--includes')
         else:
             args = ('--null', '--file', path, '--list')