Add course-specific URL overrides for social sharing icons on student dashboard

- sharing enabled for custom URLs only if URL actually specified

cms/djangoapps/models/settings/course_metadata.py

@@ -69,6 +69,11 @@ class CourseMetadata(object):
         if not settings.FEATURES.get('ENABLE_MOBILE_SOCIAL_FACEBOOK_FEATURES'):
             filtered_list.append('facebook_url')
 
+        # Do not show social sharing url field if the feature is disabled.
+        if (not settings.FEATURES.get('DASHBOARD_SHARE_SETTINGS') or
+                not settings.FEATURES.get("DASHBOARD_SHARE_SETTINGS").get("CUSTOM_COURSE_URLS")):
+            filtered_list.append('social_sharing_url')
+
         return filtered_list
 
     @classmethod