If we want to allow plugins to implement EEPROM storage, it is best if we don't
do anything with EEPROM in the core firmware. As such, remove the
`Layer.defaultLayer` call from `Kaleidoscope.setup`.
With that gone, the `keymap_count` argument is obsolete, so drop it from
`Kaleidoscope.setup()` - but we keep an temporary `setup()` with the old arity,
so that plugins can be updated at a slower pace.
Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>