A2DP: Clear local pending flags while AV is stable

There was a timing issue that the local pending state was cleared, AV
state was transitioning from started to opened, and was still saw as
started before entered the opened state. This caused a mismatched
between Bluetooth stack and audio HAL, and since we would clear those
local pending flags while entring opened state, it was redundant to
clear the state before the transition.

Bug: 140609685
Test: A2DP playback manually
Change-Id: Ie60bc9c432faa5038340f57da18282255ea5c7c4