Reverse e140122202

- remove temporary fix for MemorySanitizer:
  setting p->u.array.count to 0 silenced a warning in JS_GetPropertyValue on a
  hacky test agains the length of fast_array object.
  This hack was removed by commit c3635861f6.

quickjs.c

@@ -14774,8 +14774,6 @@ static JSValue js_build_mapped_arguments(JSContext *ctx, int argc,
     if (JS_IsException(val))
         return val;
     p = JS_VALUE_GET_OBJ(val);
-    p->u.array.u.values = NULL;
-    p->u.array.count = 0;
 
     /* add the length field (cannot fail) */
     pr = add_property(ctx, p, JS_ATOM_length,