users should remove former Go installation folder

## What does this MR do?

It ensure users installing or updating from source will remove their former Go installation folder in `/usr/local/go`, to avoid raising errors that could lead to new issues being created.

## Are there points in the code the reviewer needs to double check?

1. The `rm -rf` should not be verbose if folder does not exists.
1. May a user have some kind of configuration files in this folder ?

## Why was this MR needed?

I did faced the error, that led me to the solution stated here : https://gitlab.com/gitlab-org/gitlab-workhorse/issues/29#note_4155517

gitlab-org/gitlab-workhorse#29

See merge request !6602