drm/edid/firmware: drop drm_kms_helper.edid_firmware backward compat

Since the edid_firmware module parameter was moved from
drm_kms_helper.ko to drm.ko in v4.15, we've had a backwards
compatibility helper in place, with a DRM_NOTE() suggesting to migrate
to drm.edid_firmware. This was added in commit ac6c35a4 ("drm: add
backwards compatibility support for drm_kms_helper.edid_firmware").

More than five years and 30+ kernel releases later, drop the backward
compatibility.

v2: Drop the warnings too

Acked-by: Daniel Vetter <daniel@ffwll.ch>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231114151406.61230-1-jani.nikula@intel.com