This patch:
- Rename some files( `.md` to `.en-us.md`), fix missed translation copy
- Update link which shoud be refer to `../hacking-on-gitea/` instead of
`../make/` (outdated)
- Update `_redirects`:
- redirect `/{zh-cn|fr-fr}/make/` to `../hacking-on-gitea/`
- redirect `/zh-cn/third-party-tools/` to `/zh-cn/integrations/`
- Delete duplicated/outdated files.
- Update menu `weight` of developers.zh-cn.md
Signed-off-by: Xinyu Zhou <i@sourcehut.net>
