[SP37] Change requirement of older event callback.

Currently, vendors are asked to duplicate old events to onEvent()
and onEvent_1_1(). This is not the typically way other modules
would do. Thus, remove the requirement of duplicate events,
and replace it with only firing onEvent_1_1 when feasible.

Note no VTS is added currently, from vendor feedback, there is
no reliable way to guarantee the callbacks will be called in the
test.

Test: hidl-gen -L hash -r android.hardware:hardware/interfaces \
      android.hardware.tetheroffload.control@1.1
Bug: 149467454
Merged-In: I75c1a7788e5d48fb3e2836d54b4fd854c0247214
Change-Id: I75c1a7788e5d48fb3e2836d54b4fd854c0247214
  (cherry-picked from ag/14408065)

tetheroffload/control/1.1/ITetheringOffloadCallback.hal

@@ -26,8 +26,8 @@ import OffloadCallbackEvent;
 interface ITetheringOffloadCallback extends @1.0::ITetheringOffloadCallback {
     /**
      * Called when an asynchronous event is generated by the hardware
-     * management process. Events which are common for 1.0 and 1.1 HAL
-     * MUST be fired on both 1.0 and 1.1 callback.
+     * management process. Implementations that report events via this callback
+     * should not invoke onEvent of 1.0 HAL.
      */
     oneway onEvent_1_1(OffloadCallbackEvent event);
 };