Changed the property used to define a layer name for displays from
"label" (which affects other things in Zephyr and is deprecated) to
"display-name". (It cannot be named simply "name", because that has
special meaning in newer versions of the devicetree compiler.)
"label" is still supported as a fallback, so no changes need to be made
to existing keymaps.
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.
