Fix kotlinc warnings in EasterEgg.

- Remove unused parameters / method
- Wrap uses nullable bitmap with "?.let {" and sadly !! as it is
  in fact theoretically possible that bitmap becomes null due to a
  call from a different thread.
- Run ktlint autofix up.

Bug: 112638508
Test: make -j EasterEgg
Change-Id: Idab21176ec9e4e61751a87c4aeafe3966ed10a8c