When "Show Cursor" is unchecked, the Drivers Editor would still display
the vertical line representing the cursor x.
Probably overseen in {rB65072499c65a} (historically the vertical line
could represent either the current frame of the cursor X in drawing, but
this is now much more separate).
There is no point in seeing part of the cursor in the Drivers Editor if
this is disabled.
Also correct outdated comments.
ref. T91157
Maniphest Tasks: T91157
Differential Revision: https://developer.blender.org/D12391
6f29801f1b