[docs] Outdated version entry should be cleaned up and removed from version table

[smeng9]

Related page

https://mui.com/versions/

Kind of issue

Other

Issue description

We should not have a random minor version 5.0.6 (that is not up to date with latest v5) showing up in the version table.

This will give reader a false feeling that the latest version of v5 is v5.0.6

Context

The branch named v5.0.6 in https://github.com/mui/material-ui-docs/branches can probably be removed.

Search keywords: released versions