drm/i915/bios: remove some unused leftover declarations

Remove some unused declarations probably left behind after some
refactoring.

Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231221105414.1518267-1-jani.nikula@intel.com