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.

[afercia]

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.

[afercia]

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

[SergeyBiryukov]

In 33456:

Replace empty table header with a table cell.

props afercia.
fixes #33047.