Way can be reasonably assumed to not be covered.

[matkoniecz]

Currently on editing road without covered tag "Covered Unknown" is presented. It encourages adding useless tag "covered=no".

Triggered by

I just added a highway=service surface=gravel and then i saw id ask if it was covered= yes or no... or i saw the checkbox popped up.
It's very obviously outside and not covered, does that need to be specified?
obviously if it was covered it should be tagged as such but the no seems a bit much.

from https://discord.com/channels/413070382636072960/782592770849505281/810068042876452875

Basically redo of openstreetmap/iD#2220

It would be better to display "Assumed to be no" instead of "Unknown".

[quincylvania]

This sounds fine. Note that the Covered field also won't be shown by default on the Service Road preset in the next release: #46