[cleanup] Remove obsolete ElementsAccessor::kCopyToEnd.

Also generally cleanup the Copy* code in elements.cc a bit.

Bug: v8:9183
Change-Id: I4a56db1f0b382a4b9583cae3b47e4ce572393d9e
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1634249Reviewed-by: Simon Zünd <szuend@chromium.org>
Commit-Queue: Benedikt Meurer <bmeurer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#61908}

src/objects/elements.h

@@ -66,15 +66,6 @@ class ElementsAccessor {
   // element that is non-deletable.
   virtual void SetLength(Handle<JSArray> holder, uint32_t new_length) = 0;
 
-  // If kCopyToEnd is specified as the copy_size to CopyElements, it copies all
-  // of elements from source after source_start to the destination array.
-  static const int kCopyToEnd = -1;
-  // If kCopyToEndAndInitializeToHole is specified as the copy_size to
-  // CopyElements, it copies all of elements from source after source_start to
-  // destination array, padding any remaining uninitialized elements in the
-  // destination array with the hole.
-  static const int kCopyToEndAndInitializeToHole = -2;
-
   // Copy all indices that have elements from |object| into the given
   // KeyAccumulator. For Dictionary-based element-kinds we filter out elements
   // whose PropertyAttribute match |filter|.