[cleanup] Remove unused array iterator private symbols

R=gsathya@chromium.org

Change-Id: Ia03ec888617a492720c78b6c105323182fec351e
Reviewed-on: https://chromium-review.googlesource.com/922784Reviewed-by: Sathya Gunasekaran <gsathya@chromium.org>
Commit-Queue: Adam Klein <adamk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#51318}

src/heap-symbols.h

@@ -221,9 +221,6 @@
   V(zero_string, "0")
 
 #define PRIVATE_SYMBOL_LIST(V)              \
-  V(array_iteration_kind_symbol)            \
-  V(array_iterator_next_symbol)             \
-  V(array_iterator_object_symbol)           \
   V(call_site_frame_array_symbol)           \
   V(call_site_frame_index_symbol)           \
   V(console_context_id_symbol)              \