package/python-twisted: Needs python 3

From the twisted-21.2.0 release notes:

Deprecations and Removals

 - Support for Python 2.7 has been removed.  Twisted now supports only
   Python versions 3.5/3.6/3.7.

https://github.com/twisted/twisted/releases/tag/twisted-21.2.0

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/python-twisted/Config.in

@@ -1,5 +1,6 @@
 config BR2_PACKAGE_PYTHON_TWISTED
 	bool "python-twisted"
+	depends on BR2_PACKAGE_PYTHON3
 	select BR2_PACKAGE_PYTHON_INCREMENTAL
 	select BR2_PACKAGE_PYTHON_ATTRS # runtime
 	select BR2_PACKAGE_PYTHON_AUTOMAT # runtime

support/testing/tests/package/test_python_twisted.py

@@ -21,15 +21,6 @@ class TestPythonTwisted(TestPythonPackageBase):
         self.assertEqual(exit_code, 0)
 
 
-class TestPythonPy2Twisted(TestPythonTwisted):
-    __test__ = True
-    config = TestPythonTwisted.config + \
-        """
-        BR2_PACKAGE_PYTHON=y
-        BR2_PACKAGE_PYTHON_TWISTED=y
-        """
-
-
 class TestPythonPy3Twisted(TestPythonTwisted):
     __test__ = True
     config = TestPythonTwisted.config + \