Remove or fix broken links for community maintained installs

### Page link:

https://github.com/bazelbuild/bazel/blob/5079890c10e90eadbe70c2957f2dc14d48a881a8/site/en/install/index.md

### Problem description (include actual vs expected text, if applicable):

- CentOS 6 is no longer supported
- Gentoo link is broken, no longer packaged
- OpenSUSE link is broken, should update to https://software.opensuse.org/package/bazel
- Parabola link indicates no longer packaged

### Where do you see this issue? (include link to specific section of the page, if applicable)

_No response_

### Any other information you'd like to share?

Can make a pull request to remove broken links

Open site/en/install/index.md at the referenced revision and inspect the community-maintained install links. Remove the CentOS 6, Gentoo, and Parabola entries if they are no longer valid, update the OpenSUSE link to the URL in the issue, and verify the resulting page links.

Written by the indexing model from the issue text.