Feature flag: remove USE_SPHINX_BUILDERS

We can safely remove this feature flag since it's marked as `default_true=True`
and `future_default_true=True` in both platforms. This means that it applies to
all the projects.

Author: humitos

readthedocs/doc_builder/backends/sphinx.py

@@ -370,27 +370,21 @@ class HtmlBuilder(BaseSphinx):
 
     def __init__(self, *args, **kwargs):
         super().__init__(*args, **kwargs)
-        self.sphinx_builder = 'readthedocs'
-        if self.project.has_feature(Feature.USE_SPHINX_BUILDERS):
-            self.sphinx_builder = 'html'
+        self.sphinx_builder = "html"
 
 
 class HtmlDirBuilder(HtmlBuilder):
 
     def __init__(self, *args, **kwargs):
         super().__init__(*args, **kwargs)
-        self.sphinx_builder = 'readthedocsdirhtml'
-        if self.project.has_feature(Feature.USE_SPHINX_BUILDERS):
-            self.sphinx_builder = 'dirhtml'
+        self.sphinx_builder = "dirhtml"
 
 
 class SingleHtmlBuilder(HtmlBuilder):
 
     def __init__(self, *args, **kwargs):
         super().__init__(*args, **kwargs)
-        self.sphinx_builder = 'readthedocssinglehtml'
-        if self.project.has_feature(Feature.USE_SPHINX_BUILDERS):
-            self.sphinx_builder = 'singlehtml'
+        self.sphinx_builder = "singlehtml"
 
 
 class LocalMediaBuilder(BaseSphinx):

readthedocs/projects/models.py

@@ -1944,7 +1944,6 @@ def add_features(sender, **kwargs):
     LIST_PACKAGES_INSTALLED_ENV = "list_packages_installed_env"
     VCS_REMOTE_LISTING = "vcs_remote_listing"
     SPHINX_PARALLEL = "sphinx_parallel"
-    USE_SPHINX_BUILDERS = "use_sphinx_builders"
     CANCEL_OLD_BUILDS = "cancel_old_builds"
     DONT_CREATE_INDEX = "dont_create_index"
     USE_RCLONE = "use_rclone"
@@ -2112,10 +2111,6 @@ def add_features(sender, **kwargs):
             SPHINX_PARALLEL,
             _('Sphinx: Use "-j auto" when calling sphinx-build'),
         ),
-        (
-            USE_SPHINX_BUILDERS,
-            _("Sphinx: Use regular sphinx builders instead of custom RTD builders"),
-        ),
         (
             CANCEL_OLD_BUILDS,
             _(

readthedocs/rtd_tests/tests/test_doc_builder.py

@@ -263,11 +263,6 @@ def test_multiple_conf_py(
 
     @mock.patch('readthedocs.doc_builder.config.load_config')
     def test_use_sphinx_builders(self, load_config):
-        feature = get(
-            Feature,
-            feature_id=Feature.USE_SPHINX_BUILDERS,
-        )
-
         config_data = {'version': 2, 'sphinx': {'configuration': 'docs/conf.py'}}
         load_config.side_effect = create_load(config_data)
         config = load_yaml_config(self.version)
@@ -277,27 +272,6 @@ def test_use_sphinx_builders(self, load_config):
             build_env=self.build_env,
             config=config,
         )
-        builder = HtmlBuilder(
-            build_env=self.build_env,
-            python_env=python_env,
-        )
-        self.assertEqual(builder.sphinx_builder, 'readthedocs')
-
-        builder = HtmlDirBuilder(
-            build_env=self.build_env,
-            python_env=python_env,
-        )
-        self.assertEqual(builder.sphinx_builder, 'readthedocsdirhtml')
-
-        builder = SingleHtmlBuilder(
-            build_env=self.build_env,
-            python_env=python_env,
-        )
-        self.assertEqual(builder.sphinx_builder, 'readthedocssinglehtml')
-
-        # Add the feature to use the regular builders
-        feature.projects.add(self.project)
-
         builder = HtmlBuilder(
             build_env=self.build_env,
             python_env=python_env,