[fullcodegen] Remove the hacky %_FastOneByteArrayJoin intrinsic.

src/js/array.js

Index: src/js/array.js
diff --git a/src/js/array.js b/src/js/array.js
index 28d964eaae87a36e05585a8755938a5fb3feb0d0..b8cf3ff5d222a3fb65266a9539890b218b1b30d4 100644
--- a/src/js/array.js
+++ b/src/js/array.js
@@ -209,8 +209,6 @@ function Join(array, length, separator, convert) {
         elements[elements_length++] = e;
       }
       elements.length = elements_length;
-      var result = %_FastOneByteArrayJoin(elements, '');
-      if (!IS_UNDEFINED(result)) return result;
       return %StringBuilderConcat(elements, elements_length, '');
     }
     // Non-empty separator case.
@@ -233,9 +231,6 @@ function Join(array, length, separator, convert) {
         elements[i] = e;
       }
     }
-    var result = %_FastOneByteArrayJoin(elements, separator);
-    if (!IS_UNDEFINED(result)) return result;
-
     return %StringBuilderJoin(elements, length, separator);
   } finally {
     // Make sure to remove the last element of the visited array no
@@ -447,9 +442,6 @@ function InnerArrayJoin(separator, array, length) {
     separator = TO_STRING(separator);
   }
 
-  var result = %_FastOneByteArrayJoin(array, separator);
-  if (!IS_UNDEFINED(result)) return result;
-
   // Fast case for one-element arrays.
   if (length === 1) {
     var e = array[0];