Cleanup migrated experiments

[Arlodotexe]

Background

• SegmentedControl was ported to the stable repo in Porting Segmented Windows#157
• StackedNotificationsBehavior was ported to the stable repo in StackedNotificationsBehavior port Windows#170

Problem

These controls are still present in Labs and need to be removed. Further iteration will happen in the stable repo.

Solution

Remove the SegmentedControl and StackedNotificationBehavior from Labs.

[michael-hawker]

@Arlodotexe should we just do this quick before #485 as that PR was trying to fix some things in the Behaviors that we fixed in the Windows repo already?