Remove max automatic backups setting

We just always create up to 4 now to simplify it, given the addition of syncing
is going to make this section pretty busy.

app/src/main/java/eu/kanade/tachiyomi/Migrations.kt

@@ -295,9 +295,6 @@ object Migrations {
                 }
             }
             if (oldVersion < 84) {
-                if (backupPreferences.numberOfBackups().get() == 1) {
-                    backupPreferences.numberOfBackups().set(2)
-                }
                 if (backupPreferences.backupInterval().get() == 0) {
                     backupPreferences.backupInterval().set(12)
                     BackupCreateJob.setupTask(context)