Remove static from the listener.

To support Multi-SIM and multi-IMS stack use cases, we should have
multiple instances of ImsManager. And each instance may need a
separate isntance of the Listener if it needs to invoke non-static
methods or access any fields of the ImsManager.

Test: Successful compilation with this change.
Change-Id: Idf4de1232ea54fef03a9e4a7ce1d98b8df841291