ash: Delete obsolete comment in SessionController referring to mustash

There's no longer anything to do here.

Bug: 729808
Change-Id: Ic0cf93abdcbdfdbfc2392df1a46e1c129a5166fd
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1752286
Commit-Queue: James Cook <jamescook@chromium.org>
Commit-Queue: Xiyuan Xia <xiyuan@chromium.org>
Auto-Submit: James Cook <jamescook@chromium.org>
Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#686485}

ash/public/cpp/session/session_controller.h

@@ -77,9 +77,6 @@ class ASH_PUBLIC_EXPORT SessionController {
   // Adds a countdown timer to the system tray menu and creates or updates a
   // notification saying the session length is limited (e.g. a public session in
   // a library). Setting |length_limit| to zero removes the notification.
-  // NOTE: Chrome enforces the limit, not ash. Ash could enforce it if local
-  // state prefs and user activity monitoring were available under mustash.
-  // http://crbug.com/729808
   virtual void SetSessionLengthLimit(base::TimeDelta length_limit,
                                      base::TimeTicks start_time) = 0;