Make FastJobStorage synchronous again.

app/src/main/java/org/thoughtcrime/securesms/jobmanager/JobController.java

@@ -77,11 +77,6 @@ class JobController {
     notifyAll();
   }
 
-  @WorkerThread
-  synchronized void flush() {
-    jobStorage.flush();
-  }
-
   @WorkerThread
   synchronized void submitNewJobChain(@NonNull List<List<Job>> chain) {
     chain = Stream.of(chain).filterNot(List::isEmpty).toList();

app/src/main/java/org/thoughtcrime/securesms/jobmanager/JobManager.java

@@ -320,10 +320,7 @@ public class JobManager implements ConstraintObserver.Notifier {
   public void flush() {
     CountDownLatch latch = new CountDownLatch(1);
 
-    runOnExecutor(() -> {
-      jobController.flush();
-      latch.countDown();
-    });
+    runOnExecutor(latch::countDown);
 
     try {
       latch.await();

app/src/main/java/org/thoughtcrime/securesms/jobmanager/persistence/JobStorage.java

@@ -11,9 +11,6 @@ public interface JobStorage {
   @WorkerThread
   void init();
 
-  @WorkerThread
-  void flush();
-
   @WorkerThread
   void insertJobs(@NonNull List<FullSpec> fullSpecs);