[in-place weak refs] Remove references to BytecodeArray::WeakBodyDescriptor

It's the same as BytecodeArray::BodyDescriptor.

BUG=v8:7308

Change-Id: I3821108cc6cc577261ce58cd034e21dfbe2c3c87
Reviewed-on: https://chromium-review.googlesource.com/1227126Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Marja Hölttä <marja@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55946}

src/heap/concurrent-marking.cc

@@ -264,9 +264,9 @@ class ConcurrentMarkingVisitor final
 
   int VisitBytecodeArray(Map* map, BytecodeArray* object) {
     if (!ShouldVisit(object)) return 0;
-    int size = BytecodeArray::BodyDescriptorWeak::SizeOf(map, object);
+    int size = BytecodeArray::BodyDescriptor::SizeOf(map, object);
     VisitMapPointer(object, object->map_slot());
-    BytecodeArray::BodyDescriptorWeak::IterateBody(map, object, size, this);
+    BytecodeArray::BodyDescriptor::IterateBody(map, object, size, this);
     object->MakeOlder();
     return size;
   }

src/objects/code.h

@@ -797,8 +797,6 @@ class BytecodeArray : public FixedArrayBase {
   static const int kMaxLength = kMaxSize - kHeaderSize;
 
   class BodyDescriptor;
-  // No weak fields.
-  typedef BodyDescriptor BodyDescriptorWeak;
 
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(BytecodeArray);