R1:8052ab84bfd8

Remove "^" (Prev) and "V" (Next) actions on Differential inline comments

Summary:
Ref T12616. Fixes T12715. I suspect these are very rarely used. (I think you tried to get rid of them before but I pushed back since we couldn't really offer great alternatives at the time?)

Now that the code is in a better place:

- Click an inline's header (just the colored part) to select it with the keyboard selection cursor.
- Click again to deselect it.
- You can use "n" and "p" to jump to comments, so "click +…