Hide code links on release page if user cannot read code (#29064)

Hide code links on release page if user cannot read code (#29064)

On the release list page, if the user doesn't have the permission to
read code, the code links will lead to 404 pages or api errors:

<img width="1297" alt="image"
src="https://github.com/go-gitea/gitea/assets/9418365/a74fbc63-6dd6-43c6-853c-28acdbfdcb4e">

After this PR:

<img width="1297" alt="image"
src="https://github.com/go-gitea/gitea/assets/9418365/a626373d-c2df-40a9-8fed-1b12ff6bc56f">

And this PR also removed some dead code. After #23465, the tag list page
has an independent template, and all `IsTag` in the release list
template are always false.