Draft: Delete superfluous gitaly deps in verify image

What does this merge request do and why?

This is just another test.

Similar to !3752 (merged), this removes intermediate compilation targets from gitaly’s /home/gdk/gdk/gitaly/_build/ directory.

See this comment in the Makefile of gitaly, which says:

By default, intermediate targets get deleted automatically after a successful
build. We do not want that though: there's some precious intermediate targets
like our `*.version` targets which are required in order to determine whether
a dependency needs to be rebuilt.

We might be careful to keep .version files for the update verify job but there are currently none in the intermediate directory, unlike in the deps directory.

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

Impacted categories

The following categories relate to this merge request:

• gdk-reliability - e.g. When a GDK action fails to complete.
• gdk-usability - e.g. Improvements or suggestions around how the GDK functions.
• gdk-performance - e.g. When a GDK action is slow or times out.

Merge request checklist

• This change is backward compatible. If not, please include steps to communicate to our users.
• Tests added for new functionality. If not, please raise an issue to follow-up.
• Documentation added/updated, if needed.
• Announcement added, if change is notable.
• gdk doctor test added, if needed.
• Add the ~highlight label if this MR should be included in the CHANGELOG.md.