drm/bridge: Drop drm_bridge_chain_mode_fixup

There are no users left of drm_bridge_chain_mode_fixup() and we
do not want to have this function available, so drop it.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Reviewed-by: Maxime Ripard <mripard@kernel.org>
Reviewed-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Maxime Ripard <mripard@kernel.org>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Signed-off-by: Robert Foss <rfoss@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20240531-bridge_chain_mode-v1-2-8b49e36c5dd3@ravnborg.org