[test] Disable --force-slow-path for mjsunit/es6/array-iterator-turbo

This test expects certain functions to be optimized, which does not
happen if we force array objects onto the slow path.

Bug: v8:7122
Change-Id: I716954fff564f1c4f0782b3452557ec89a3b4307
Reviewed-on: https://chromium-review.googlesource.com/796860
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49736}

test/mjsunit/es6/array-iterator-turbo.js

@@ -3,7 +3,7 @@
 // found in the LICENSE file.
 
 // Flags: --turbo-escape --allow-natives-syntax --no-always-opt
-// Flags: --opt --turbo-filter=*
+// Flags: --opt --turbo-filter=* --no-force-slow-path
 
 "use strict";