use a background thread for deleting CalDAV events after disabling sync

app/src/main/kotlin/com/simplemobiletools/calendar/pro/activities/SettingsActivity.kt

@@ -182,10 +182,13 @@ class SettingsActivity : SimpleActivity() {
             config.caldavSync = false
             settings_manage_synced_calendars_holder.beGone()
             settings_caldav_pull_to_refresh_holder.beGone()
+
+            Thread {
                 config.getSyncedCalendarIdsAsList().forEach {
                     CalDAVHandler(applicationContext).deleteCalDAVCalendarEvents(it.toLong())
                 }
                 dbHelper.deleteEventTypesWithCalendarId(config.caldavSyncedCalendarIDs)
+            }.start()
         }
     }