cmd-cloud-prune: remove the unneeded exception

This exception was not supposed to be added there since that
check was just added to make sure there isn't any build
artifacts in meta.json top-level keys that is in unsupported list.
So far, we only prune aws and gcp. There are many top-level keys
that are not artifacts-related so this check would throw the exception
when not needed.

Author: gursewak1997

src/cmd-cloud-prune

@@ -225,8 +225,6 @@ def get_supported_images(meta_json):
             raise Exception(f"The platform {key} is not supported")
         if key in SUPPORTED:
             images[key] = meta_json[key]
-        else:
-            raise Exception(f"The platform {key} is neither in supported nor unsupported artifacts.")
     return images