Allow NONE service class in terminal based call waiting

- *43# and #43# MMI code can deliver a call waiting update request with
  a NONE service class
- These MMI code should be handled as the same way with a call waiting
  UI, but CallWaitingController directly returned it
- Aligning with ImsPhoneMmiCode and GsmMmiCode, allow a NONE service
  class also for terminal based call waiting in CallWaitingController

Bug: 433146190
Test: atest FrameworksTelephonyTests
Test: Manual test on Telstra AU
Flag: EXEMPT BUGFIX

Change-Id: Iededbbddfb38ec1b1f1fbc7d611470a4da502b56
Signed-off-by: taesoonpark <taesoonpark@google.com>