Revert "AudioSystem: Ensure onNewService callback is complete before returning service"

This reverts commit 9fb6f3dc.

No longer needed because of commit
ccbb7422
ServiceSingleton: Stricter onNewService callback handling

Flag: EXEMPT bugfix
Test: atest WvtsDeviceTestCases:com.google.android.wvts.MediaDrmParameterizedTests#testResourceRatingTierNumKeys[L1] --iterations=100 -- --abi arm64-v8a
Bug: 403676413
Change-Id: Ic4b49e9176ab27d54459a359f203c1517723124d