qmk_firmware/docs/ChangeLog/20190830/PR6299.md

• Migrating ACTION_BACKLIGHT_*() entries in fn_actions to BL_ keycodes
  • fn_actions is deprecated, and its functionality has been superseded by direct keycodes and process_record_user()
  • All keymaps using these actions have had the relevant KC_FN* keys replaced with the equivalent BL_* keys
  • If you currently use KC_FN* you will need to replace fn_actions with the custom keycode and macro features