Revert "[FAL-23] Enable ORGANIZATIONS_APP feature flag by default."

Enabling the organizations app means that users have to go to django
admin and create organizations before they can start creating new
courses in the Studio. We don't want users to have to fiddle with django
admin before being able to use the Studio.

This reverts commit 9bd5fe4.

instance/models/mixins/openedx_config.py

@@ -256,7 +256,6 @@ def _get_configuration_variables(self):
                 "ENABLE_THIRD_PARTY_AUTH": True,
                 "ENABLE_XBLOCK_VIEW_ENDPOINT": True,
                 "ENABLE_SYSADMIN_DASHBOARD": True,
-                "ORGANIZATIONS_APP": True,
                 "PREVIEW_LMS_BASE": self.instance.lms_preview_domain,
                 "REQUIRE_COURSE_EMAIL_AUTH": False,
                 "USE_MICROSITES": False,