lint: Ban use of deprecated assertEquals.

tools/lint-all

@@ -326,6 +326,8 @@ def build_custom_checkers(by_lang):
         {'pattern': "^\s+[#]\w",
          'strip': '\n',
          'description': 'Missing whitespace after "#"'},
+        {'pattern': "assertEquals[(]",
+         'description': 'Use assertEqual, not assertEquals (which is deprecated).'},
         {'pattern': "== None",
          'exclude': 'tools/lint-all',
          'description': 'Use `is None` to check whether something is None'},

zerver/lib/test_classes.py

@@ -292,7 +292,7 @@ class ZulipTestCase(TestCase):
         # type: (str, bytes) -> None
         response = self.client_get(url)
         data = b"".join(response.streaming_content)
-        self.assertEquals(result, data)
+        self.assertEqual(result, data)
 
     def assert_json_success(self, result):
         # type: (HttpResponse) -> Dict[str, Any]