The installation link has changed from /installation/ to /install/. This
commit will update all the remaining links that are missing.

Marcel Amirault authored 5 years ago and Achilleas Pipinellis committed 5 years ago

Previously, we used brackets to denote the tier badges,
but this made Kramdown, the docs site Markdown renderer,
show many warnings when building the site. This is now
fixed by using parentheses instead of square brackets.

This was caused by [PREMIUM] looking like a link to
Kramdown, which couldn't find a URL there.

See:
- https://gitlab.com/gitlab-com/gitlab-docs/merge_requests/484
- https://gitlab.com/gitlab-org/gitlab-ce/issues/63800

Using Geo with source-based installs was deprecated in GitLab 11.5.

This commit removes this support now that the deprecation notice has
been in place for quite a few releases.