Fix activity coordinator links to conceptual docs

Author: alvinashcraft

sdk-api-src/content/_activity_coordinator/index.md

@@ -20,10 +20,10 @@ To develop for Activity Coordinator, you need these headers:
 
 For programming guidance for this technology, see:
 
-* [Activity Coordinator overview](/windows/win32/activity_coordinator/activity-coordinator-api-overview.md)
-* [Activity Coordinator API and terminology](/windows/win32/activity_coordinator/activity-coordinator-api-and-terminology.md)
-* [Choosing the right Activity Coordinator policy](/windows/win32/activity_coordinator/choosing-the-right-activity-coordinator-policy.md)
-* [Activity Coordinator example project](/windows/win32/activity_coordinator/activity-coordinator-example-project.md)
+* [Activity Coordinator overview](/windows/win32/activity_coordinator/activity-coordinator-api-overview)
+* [Activity Coordinator API and terminology](/windows/win32/activity_coordinator/activity-coordinator-api-and-terminology)
+* [Choosing the right Activity Coordinator policy](/windows/win32/activity_coordinator/choosing-the-right-activity-coordinator-policy)
+* [Activity Coordinator example project](/windows/win32/activity_coordinator/activity-coordinator-example-project)
 
 For general Win32 programming guidance, see: