Remove 3.0 also

Author: ericholscher

readthedocs/settings/base.py

@@ -370,6 +370,8 @@ def USE_PROMOS(self):  # noqa
     DOCKER_DEFAULT_VERSION = 'latest'
     DOCKER_IMAGE = '{}:{}'.format(DOCKER_DEFAULT_IMAGE, DOCKER_DEFAULT_VERSION)
     DOCKER_IMAGE_SETTINGS = {
+        # A large number of users still have this pinned in their config file.
+        # We must have documented it at some point.
         'readthedocs/build:2.0': {
             'python': {
                 'supported_versions': [2, 2.7, 3, 3.5],
@@ -379,15 +381,6 @@ def USE_PROMOS(self):  # noqa
                 },
             },
         },
-        'readthedocs/build:3.0': {
-            'python': {
-                'supported_versions': [2, 2.7, 3, 3.3, 3.4, 3.5, 3.6],
-                'default_version': {
-                    2: 2.7,
-                    3: 3.6,
-                },
-            },
-        },
         'readthedocs/build:4.0': {
             'python': {
                 'supported_versions': [2, 2.7, 3, 3.5, 3.6, 3.7],