Deleting navigation links could be easier

[talldan]

Discussed in #21450
Related: #18208

Is your feature request related to a problem? Please describe.
As a user, if I accidentally add a navigation link to the navigation block, removing it is not completely obvious or simple to achieve.

Currently the options are:

• Click the more menu and select remove block
• Remember the remove block shortcut and use that.

Describe the solution you'd like
If the navigation link is empty, pressing delete or backspace could remove the link.

#18208 suggests being able to add links using Enter, so deleting seems like it would naturally fit in with that.

Describe alternatives you've considered
The block navigator is another place where deleting could be surface, but I think it makes sense to have easy ways to achieve deletion in both the block interface and the navigator.