Squash runnables in onBootCompleted (1/n)

Some code clean-up to makes it easier to register
OnPropertiesChangedListener there in the next patch.

Bug: 147712943
Test: atest StagedRollbackTest RollbackTest
Change-Id: I46d08fe2715b7c6a08d9a6d862dc0ab0dd3de12c

services/core/java/com/android/server/rollback/RollbackManagerServiceImpl.java

@@ -511,11 +511,10 @@ class RollbackManagerServiceImpl extends IRollbackManager.Stub {
 
     @AnyThread
     void onBootCompleted() {
-        getHandler().post(() -> updateRollbackLifetimeDurationInMillis());
-        // Also posts to handler thread
-        scheduleExpiration(0);
-
         getHandler().post(() -> {
+            updateRollbackLifetimeDurationInMillis();
+            runExpiration();
+
             // Check to see if any rollback-enabled staged sessions or staged
             // rollback sessions been applied.
             List<Rollback> enabling = new ArrayList<>();