drm/i915/frontbuffer: remove obsolete comment about mark busy/idle

This no longer exists.
Reviewed-by: NChris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: NJani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190606122203.13416-4-jani.nikula@intel.com

drivers/gpu/drm/i915/intel_frontbuffer.c

@@ -53,14 +53,8 @@
  * busyness. There is no direct way to detect idleness. Instead an idle timer
  * work delayed work should be started from the flush and flip functions and
  * cancelled as soon as busyness is detected.
- *
- * Note that there's also an older frontbuffer activity tracking scheme which
- * just tracks general activity. This is done by the various mark_busy and
- * mark_idle functions. For display power management features using these
- * functions is deprecated and should be avoided.
  */
 
-
 #include "i915_drv.h"
 #include "intel_dp.h"
 #include "intel_drv.h"