Use VolumeControlService instead of proxy

LeAudioService will no longer register VolumeControlService but will
directly call VolumeControlService.

Factory seems to be how A2dp talks to avrcpVolumeManager. I reproduced
how it works on LeAudio

Also the `Intent.resolveSystemService` is a hidden API and cannot be
called once bluetooth will be a mainline module, that's why i submit
this patch

Test: atest BluetoothInstrumentationTests
Bug: 200200870
Tag: #refactor
Change-Id: I4119bb794fb7f141a1994f9fa58f87684ddc22d8