S3 object parameter and bucket deletion exclusive (#21830)

Fixes ansible#21796 Prevent users from deleting buckets rather than objects by making object parameter and mode=delobj mutually exclusive in task.
https://github.com/ansible/ansible/issues/21796

lib/ansible/modules/cloud/amazon/s3.py

@@ -511,6 +511,10 @@ def main():
     if module.params.get('object'):
         obj = module.params['object']
 
+    # Bucket deletion does not require obj.  Prevents ambiguity with delobj.
+    if obj and mode == "delete":
+        module.fail_json(msg='Parameter obj cannot be used with mode=delete')
+
     # allow eucarc environment variables to be used if ansible vars aren't set
     if not s3_url and 'S3_URL' in os.environ:
         s3_url = os.environ['S3_URL']