powerpc/ps3: Remove unused os_area_db_id_video_mode

This struct is unused, which is now a build error with gcc 6:

  error: 'os_area_db_id_video_mode' defined but not used

There doesn't seem to be any good reason to keep it around so remove it,
it's in the history if anyone needs it.
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/platforms/ps3/os-area.c

@@ -194,11 +194,6 @@ static const struct os_area_db_id os_area_db_id_rtc_diff = {
 	.key = OS_AREA_DB_KEY_RTC_DIFF
 };
 
-static const struct os_area_db_id os_area_db_id_video_mode = {
-	.owner = OS_AREA_DB_OWNER_LINUX,
-	.key = OS_AREA_DB_KEY_VIDEO_MODE
-};
-
 #define SECONDS_FROM_1970_TO_2000 946684800LL
 
 /**