Simplify account notification management

app/src/main/java/eu/faircode/email/ActivitySetup.java

@@ -770,7 +770,7 @@ public class ActivitySetup extends ActivityBilling implements FragmentManager.On
                         account.id = db.account().insertAccount(account);
                         Log.i("Imported account=" + account.name);
 
-                        if (android.os.Build.VERSION.SDK_INT >= android.os.Build.VERSION_CODES.O)
+                        account.deleteNotificationChannel(context);
                         if (account.notify)
                             account.createNotificationChannel(context);
 

app/src/main/java/eu/faircode/email/EntityAccount.java

@@ -23,10 +23,8 @@ import android.app.Notification;
 import android.app.NotificationChannel;
 import android.app.NotificationManager;
 import android.content.Context;
-import android.os.Build;
 
 import androidx.annotation.NonNull;
-import androidx.annotation.RequiresApi;
 import androidx.room.Entity;
 import androidx.room.PrimaryKey;
 
@@ -105,8 +103,8 @@ public class EntityAccount extends EntityOrder implements Serializable {
         return "notification" + (account == 0 ? "" : "." + account);
     }
 
-    @RequiresApi(api = Build.VERSION_CODES.O)
     void createNotificationChannel(Context context) {
+        if (android.os.Build.VERSION.SDK_INT >= android.os.Build.VERSION_CODES.O) {
             NotificationManager nm = (NotificationManager) context.getSystemService(Context.NOTIFICATION_SERVICE);
             NotificationChannel channel = new NotificationChannel(
                     getNotificationChannelId(id), name,
@@ -114,12 +112,14 @@ public class EntityAccount extends EntityOrder implements Serializable {
             channel.setLockscreenVisibility(Notification.VISIBILITY_PRIVATE);
             nm.createNotificationChannel(channel);
         }
+    }
 
-    @RequiresApi(api = Build.VERSION_CODES.O)
     void deleteNotificationChannel(Context context) {
+        if (android.os.Build.VERSION.SDK_INT >= android.os.Build.VERSION_CODES.O) {
             NotificationManager nm = (NotificationManager) context.getSystemService(Context.NOTIFICATION_SERVICE);
             nm.deleteNotificationChannel(getNotificationChannelId(id));
         }
+    }
 
     @Override
     Long getSortId() {

app/src/main/java/eu/faircode/email/FragmentAccount.java

@@ -965,12 +965,9 @@ public class FragmentAccount extends FragmentBase {
                     EntityLog.log(context, (update ? "Updated" : "Added") + " account=" + account.name);
 
                     // Make sure the channel exists on commit
-                    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O)
-                        if (account.notify) {
-                            // Add or update notification channel
-                            account.deleteNotificationChannel(context);
+                    if (account.notify)
                         account.createNotificationChannel(context);
-                        } else if (!account.synchronize)
+                    else if (!account.synchronize)
                         account.deleteNotificationChannel(context);
 
                     List<EntityFolder> folders = new ArrayList<>();

app/src/main/java/eu/faircode/email/ServiceSynchronize.java

@@ -447,7 +447,6 @@ public class ServiceSynchronize extends LifecycleService {
                     // Start monitoring accounts
                     List<EntityAccount> accounts = db.account().getSynchronizingAccounts();
                     for (final EntityAccount account : accounts) {
-                        if (android.os.Build.VERSION.SDK_INT >= android.os.Build.VERSION_CODES.O)
                         if (account.notify)
                             account.createNotificationChannel(ServiceSynchronize.this);
                         else