Bug 40073: Remove the ./ prefix when zipping files.

When using 7-zip, the ./ prefix is added to the archive, and it breaks some consumers (e.g., Firefox when re-packing omni.ja).

I've tested it only with firefox-android, but I've seen it's used also in projects/firefox/config (in rezip). I think it'll be fine though, because we're always zipping the current directory.

Closes #40073 (closed).