[cleanup] Fix incorrect comment

Remove part of comment about returning a boolean from ReadData since the
function doesn't return anything (and hasn't for more than 8 years).

R=yangguo

Change-Id: Ie38d68ef36077d08faecc8540c5de050472142ba
Reviewed-on: https://chromium-review.googlesource.com/1174535Reviewed-by: Yang Guo <yangguo@chromium.org>
Commit-Queue: Dan Elphick <delphick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55126}

src/snapshot/deserializer.cc

@@ -323,8 +323,7 @@ HeapObject* Deserializer<AllocatorT>::GetBackReferencedObject(int space) {
   return obj;
 }
 
-// This routine writes the new object into the pointer provided and then
-// returns true if the new object was in young space and false otherwise.
+// This routine writes the new object into the pointer provided.
 // The reason for this strange interface is that otherwise the object is
 // written very late, which means the FreeSpace map is not set up by the
 // time we need to use it to mark the space at the end of a page free.