Performance improvement by avoiding running commands in docker

[williambrode]

I noticed that fyne-cross running on my gitlab CI was taking a very long time to clean directories that don't even exist. I found that because these cleans are run using docker - it takes a while just to spin up the container to run them.

### Description:

Fixes #(issue)

Checklist:

• [ ] Tests included.
• [ ] Lint and formatter run with no errors.
• [ ] Tests all pass.

Where applicable:

• [ ] Public APIs match existing style.
• [ ] Any breaking changes have a deprecation path or have been discussed.
• [ ] Updated the vendor folder (using go mod vendor).

[andydotxyz]

As noted on our chat channels, I am not sure if it was important that the old way was used - hopefully @Bluebugs, @lucor or @Jacalz can comment?

[williambrode]

This is a huge performance improvement - I think it may be worth trying unless we know a reason not to do it.

[Jacalz]

I think we've all been rather busy unfortunately. I'll try to have a look first things after my vacation.