Remove IActionBlocker.CanMove (#4449)

* Remove IActionBlocker.CanMove

Ported the remainders over to using MovementAttemptEvent which should also help make mob movement a bit faster.

* Make that check faster

Content.Shared/Stunnable/StunSystem.cs

@@ -1,3 +1,4 @@
+using Content.Shared.Movement;
 using JetBrains.Annotations;
 using Robust.Shared.GameObjects;
 
@@ -6,6 +7,18 @@ namespace Content.Shared.Stunnable
     [UsedImplicitly]
     internal sealed class StunSystem : EntitySystem
     {
+        public override void Initialize()
+        {
+            base.Initialize();
+            SubscribeLocalEvent<SharedStunnableComponent, MovementAttemptEvent>(HandleMoveAttempt);
+        }
+
+        private void HandleMoveAttempt(EntityUid uid, SharedStunnableComponent component, MovementAttemptEvent args)
+        {
+            if (component.Stunned)
+                args.Cancel();
+        }
+
         public override void Update(float frameTime)
         {
             base.Update(frameTime);