Removing some installation instructions

| Q             | A
| ------------- | ---
| Doc fix?      | no
| New docs?     | no
| Applies to    | all
| Fixed tickets | n/a

Hi guys!

This removes some duplicate installation instructions. I want less docs, without explaining less :). Duplicate like this is an opportunity to give users more paths for no reason. I'm sure we have more things like this - like details on handling parameters.yml or other things.

Thanks!
IMO, this page should only care about the SVN-specific instructions. Even people not using the installer will already have the vendors at this step if they followed the installation instructions linked at the top of this page, as they also ask to install vendors for other installation methods