add removing from apt as part of uninstalling

content/manuals/engine/install/debian.md

@@ -264,6 +264,13 @@ To upgrade Docker Engine, download the newer package files and repeat the
     $ sudo rm -rf /var/lib/containerd
     ```
 
+3.  Remove source list and keyrings
+
+    ```console
+    $ sudo rm /etc/apt/sources.list.d/docker.list
+    $ sudo rm /etc/apt/keyrings/docker.asc
+    ```
+
 You have to delete any edited configuration files manually.
 
 ## Next steps