Project download buttons always show

## What does this MR do?
Removes `hidden-xs hidden-sm` classes from `download-button` so it doesn’t hide itself individually from the rest of the `project-repo-buttons` block

## Why was this MR needed?
Fixes #23960. Not sure why this element had these classes in the first place, but at the very least we shouldn’t be hiding the Download button at the `hidden-sm` threshold since that’s still fairly large viewport and users with viewports of that size likely still want to download source code.

## Screenshots (if relevant)
Screenshots taken at ~830px width
__Before__
![before](/uploads/21955cf7a12f6eb9cfef96bbb27b7110/before.png)

__After__
![after](/uploads/c082884f225184d56a920adbc0a0a732/after.png)

## What are the relevant issue numbers?
#23960

See merge request !7405