Simplify test for the `skip` status in `html` plugin

[psss]

In #3863 a new test coverage was added which could possibly be simplified by extending the /tests/report/html test instead of exercising various restraint-only-related testcases of /tests/execute/restraint/report-result. Let's simplify the test to minimize future maintenance.

[tcornell-bus]

I did try adding it to /tests/report/html at first, but I learned that this commit would need to be undone for tmt to interpret the result: skip in a .fmf file. It looked to me like the restraint/report-result operations were the only way to force a skip result in a way that tmt would interpret.

In regards to checking for all the different status test names, I agree I think I went overboard 😅 . /tests/report/html already verifies that the other test status' are represented in the html file. I should just verify the skip tests.