drm/fourcc: Remove struct drm_format_buf_name

The structure is unused. Remove it.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210516121315.30321-5-tzimmermann@suse.de