code: private OmemoCachedDeviceList deleteStaleDevices(OmemoDevice userDevice) {
          OmemoCachedDeviceList deviceList = getOmemoStoreBackend().loadCachedDeviceList(userDevice);
          int maxAgeHours = OmemoConfiguration.getDeleteStaleDevicesAfterHours();
          return removeStaleDevicesFromDeviceList(userDevice, userDevice.getJid(), deviceList, maxAgeHours);
      }
docs: Return a copy of our deviceList, but with stale devices marked as inactive.
  Never mark our own device as stale.
  This method ignores {@link OmemoConfiguration#getDeleteStaleDevices()}!
  
  In this case, a stale device is one of our devices, from which we haven't received an OMEMO message from
  for more than {@link OmemoConfiguration#DELETE_STALE_DEVICE_AFTER_HOURS} hours.
  
  @param userDevice our OmemoDevice
  @return our altered deviceList with stale devices marked as inactive.