Set the remote shell's OOM score adjustment value via its unit file, instead of dynamically at test suite run time.

This reverts commit 9d8074d4.

The screen blanking issue has been resolved, so the workaround is not
needed any more.

Refs: #10403

We'll do one or two betas, but only once RC.

The smaller one had no shutdown button and persistence configuration :(

Closes: #10593

This validates just fine with i18nspector 0.20.1-1, I guess we'll need
a backport.

Closes: #10591

This helped me analyze a failure and find #10591.

I still sometimes see no cursor in the Greeter. A while ago we were
solving that problem on feature/jessie by disabling the cursor plugin,
and then commit 06c0abfa re-enabled it
because the bug was supposed to be fixed in some other way.

Let's see if the bug I'm seeing these days can be cured this way.

This reverts commit 29d8b7f3.