code-health: remove Sequence compatibility

collections.abc is not a part of collections since Python 3.3 [1].

1. https://docs.python.org/3/library/collections.abc.html

Part of #212

Author: DifferentialOrange

Diff for: tarantool/response.py

@@ -1,11 +1,6 @@
 # pylint: disable=C0301,W0105,W0401,W0614
 
-try:
-    # Python 3.3+
-    from collections.abc import Sequence
-except ImportError:
-    # Python 2
-    from collections import Sequence
+from collections.abc import Sequence
 
 import json
 import msgpack