Remove flaky tests from the dependency proxy suite

🌲 Context

In Maven Dependency proxy: cache miss path (!130549 - merged), we expanded the workhorse dependency proxy with options to customize how the remote file is uploaded.

At that time, we introduced a set of tests that started failing on master after a while. See #425738 (closed).

Fixing those tests will take a bit of time: we need to put some proper validation in place. To quickly fix master, we suggest in this MR to simply remove those tests.

In a subsequent MR, we will add them again along with the validation.

Removing tests seem not a great idea but actually, things are quite covered in this area. The feature that will actively use this "extension" of the dependency proxy is the dependency proxy for Maven. That part is:

• still under a feature flag. eg. not enabled anywhere.
• covered by a complete feature spec.

🤔 What does this MR do and why?

• Remove invalid_x tests from the dependency proxy suite in workhorse.

🖼 Screenshots or screen recordings

none

gear How to set up and validate locally

Run all the workhorse tests with:

$ make test

They should all pass.

🏁 MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.