Fix for not_in_use.

An image can be used by multiple containers and thus the loop will try
to remove the image from the list multiple times.

deepclean/__main__.py

@@ -52,6 +52,7 @@ def not_in_use(client, images, verbose):
     for Id in in_use_images:  # noqa: N806
         if verbose:
             print(f"Image {Id} is in use, ignoring.")
+        if Id in not_in_use_images:
             not_in_use_images.pop(Id)
     return not_in_use_images