pandora/mmi2grpc: Do not invoke WaitSource for A2DP/*/AVP/* tests

WaitSource is blocking and is causing teh AVD to initiate
the AVDTP connection after a timeout, which goes against
the test steps followed by the PTS tool

Bug: 336232163
Test: atest pts-bot
Flag: EXEMPT, test change
Change-Id: Ib6dc5da852cbffabae7d4f98d39927008b130d07