[needs-docs] Avoid duplicate use of Ctrl-D shorcut

[DelazJ]

Fixes #16702
This shortcut, also used to constrain the distance in the CAD panel, is never triggered in that case and instead tries to save the edits and remove the layer in edit.

[nyalldawson]

I'm -1 on this change. Remove layer is a very common task (much more common then using the distance constraint) and there's lots of resources, books, etc listing this shortcut. Plus it's baked into my muscle memory!

Can we change the constraint shortcut instead?

[DelazJ]

hmmmm... For consistency, we would need to find a combination that would work with (x, y, a, d) without concurrence. It happens that "Alt" is enabled for the same feature and works well except for d, where the Database menu is instead triggered --> impossible to use ctrl-D, Alt-D.
But I wonder if it does not have with some missing context instructions (or whatever it's called) on this button because pressing Ctrl-A does not select all features and as expected locks the angle while Ctrl-D tries to remove the layer instead of locking the distance (as well as Alt-D opens database menu).

Otherwise, the alternative will be to move the lock to Shift+(adxy) and use ctrl to toggle the relative placement (which currently uses Shift). @3nids?

[nyalldawson]

Superseded by #7280