Get rid of PY3 constant and codecov badge

Sadly, their service grew unreliable. :(

README.rst

@@ -10,10 +10,6 @@ attrs: Attributes Without Boilerplate
    :target: https://travis-ci.org/hynek/attrs
    :alt: CI status
 
-.. image:: https://codecov.io/github/hynek/attrs/coverage.svg?branch=master
-   :target: https://codecov.io/github/hynek/attrs?branch=master
-   :alt: Coverage
-
 .. teaser-begin
 
 ``attrs`` is the Python package that will bring back the **joy** to **writing classes** by relieving you of the drudgery of implementing object protocols (aka `dunder <http://nedbatchelder.com/blog/200605/dunder.html>`_ methods).

src/attr/_compat.py

@@ -3,7 +3,6 @@ from __future__ import absolute_import, division, print_function
 import sys
 
 
-PY3 = sys.version_info[0] == 3
 PY2 = sys.version_info[0] == 2
 
 

tests/test_make.py

@@ -10,7 +10,7 @@ from hypothesis import given
 from hypothesis.strategies import booleans, sampled_from
 
 from attr import _config
-from attr._compat import PY3
+from attr._compat import PY2
 from attr._make import (
     Attribute,
     NOTHING,
@@ -157,7 +157,7 @@ class TestAttributes(object):
     """
     Tests for the `attributes` class decorator.
     """
-    @pytest.mark.skipif(PY3, reason="No old-style classes in Py3")
+    @pytest.mark.skipif(not PY2, reason="No old-style classes in Py3")
     def test_catches_old_style(self):
         """
         Raises TypeError on old-style classes.
@@ -259,7 +259,7 @@ class TestAttributes(object):
 
         assert sentinel == getattr(C, method_name)
 
-    @pytest.mark.skipif(not PY3, reason="__qualname__ is PY3-only.")
+    @pytest.mark.skipif(PY2, reason="__qualname__ is PY3-only.")
     @given(slots_outer=booleans(), slots_inner=booleans())
     def test_repr_qualname(self, slots_outer, slots_inner):
         """