include mxcs from dangling thumbnails in service::media::iter_all

When requesting remote thumbnails over federation, we can end up with a
thumbnail in the media db without an associated original file. Because
of this, skipping thumbnails is insufficient to get a list of all MXCs.

src/database/key_value/media.rs

@@ -208,11 +208,6 @@ impl service::media::Data for KeyValueDatabase {
                     let key = MediaFileKey::new(key);
 
                     let parts = MediaFileKeyParts::try_from(&key)?;
-                    if parts.width != 0 || parts.height != 0 {
-                        // Skip thumbnails
-                        return Ok(None);
-                    };
-
                     Ok(Some((parts.mxc, parts.meta, key)))
                 })
                 .filter_map(Result::transpose),