Add getActiveDevices api

replace calls to hidden API by the systemApi.
Delete unecessary proxy around HeadsetService and Adapter

Bug: 195149213
Test: atest TelecomUnitTests
Tag: #feature
AOSP: aosp/1798127
Change-Id: Icc0b695c320d81ca5c0bfbaf7c1fac9a45f9699c
10 files changed