Reverting List extention on UserIds

Although this is how the class is used [see Update PlannerPlanDetails](https://developer.microsoft.com/en-us/graph/docs/api-reference/v1.0/api/plannerplandetails_update), the service expects a JSON object and not a JSON array. Therefore, this breaks de/serialization in the SDK.

Author: Caitlin Bales (MSFT)

src/main/java/com/microsoft/graph/models/generated/BasePlannerUserIds.java

@@ -29,7 +29,7 @@
 /**
  * The class for the Base Planner User Ids.
  */
-public class BasePlannerUserIds extends ArrayList<String> implements IJsonBackedObject {
+public class BasePlannerUserIds implements IJsonBackedObject {
 
     @SerializedName("@odata.type")
     @Expose(serialize = false)