[DOCS] Install instructions for 3006 have 'latest' which installs 3007

[dmurphy18]

Description
The install instructions for 3006, have a tab for 'latest' which 3006 is not, and should really only display major and minor versions for 3006. If you use the 'latest' tab it installs the latest 3007 which would probably be not what the user wanted

see https://docs.saltproject.io/salt/install-guide/en/3006/topics/install-by-operating-system/rhel.html#install-salt-on-redhat-rhel-8-x86-64

This same problem exists for all of the other supported OS versions of 3006.

Suggested Fix
Remove support for 'latest' tab on versions which are not the most current version of Salt, that is 3007 at the present and not 3006.

Type of documentation
Getting Started guide.

Location or format of documentation
Insert page URL if applicable.