Table headers shouldn't be empty or shouldn't be table headers

[afercia]

Spotted a couple of places where some th are empty. The th element conveys a semantic meaning and it's used by assistive technologies to establish a relationship with the related table cells. This implies a table header shouldn't be empty. Most of all, when used just for layout purposes, shouldn't be a th in the first place and a td should be used instead.

As I see it, there are two possible ways to solve this:

• add some text in the empty table headers: for example, why the th related to the 'Log Out of All Other Sessions' button is empty?
• keep it simple and just use a td

The proposed patch takes the second approach. Open to hear any thoughts and feedback.

Refreshed patch now that the user session table header has some proper text, see see 33368. See screenshot:

In 33456:

Replace empty table header with a table cell.

props afercia.
fixes #33047.