Removed "label" properties which no longer have any function.
Labels are still used as layer names and as identifiers for sending
behaviors between sides of a split keyboard, so those have been left
alone for now.
* Update docs for mod-morph
* Add unit tests for mod-morph
* Add keep-mods to DT binding
Co-authored-by: Martin Aumüller <aumuell@reserv.at>
Co-authored-by: Cem Aksoylar <caksoylar@users.noreply.github.com>
