Bug 783451 - Remove outdated FIXME comment. r=nrc,bent DONTBUILD

--HG--
extra : rebase_source : 374ea9d0259081dc532c1c64f168fbf95f6fe9eb

gfx/layers/ipc/PGrallocBuffer.ipdl

@@ -19,7 +19,6 @@ namespace layers {
  * the PGrallocBuffer constructor).
  */
 async protocol PGrallocBuffer {
-  // FIXME: Bug 783451: shouldn't be managed by PCompositor or PImageContainer
   manager PImageBridge or PLayerTransaction;
 
   /** Gralloc buffers can be "owned" by either parent or child. */