engine/install: ubuntu/rpi-os: sync uninstall with debian steps

Signed-off-by: Sebastiaan van Stijn <[email protected]>

Author: thaJeztah

content/manuals/engine/install/raspberry-pi-os.md

@@ -252,6 +252,13 @@ 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

content/manuals/engine/install/ubuntu.md

@@ -267,6 +267,13 @@ 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