When seeing a rest pattern, we used to get the remaining elements from the
iterator by calling %concat_iterable_to_array on it.  This was wrong because it
caused an observable [[Get]] for @@iterator (which the iterator may not even
provide).

This CL gets rid of the call to %concat_iterable_to_array and does the iteration
manually in a simple while-loop.  It also gets rid of %concat_iterable_to_array
itself because there aren't any other uses of it.

BUG=v8:4759
LOG=n
R=adamk@chromium.org

Review URL: https://codereview.chromium.org/1852703002

Cr-Commit-Position: refs/heads/master@{#35251}