btaa: do not initialize btaa JNI interface until gd migration is done

Stop initialize btaa JNI interface before btaa migration to gd is
finished to prevent potential issues.

Tag: #feature
Bug: 172501038
Test: atest BluetoothInstrumentationTests:com.android.bluetooth.\
btservice.activityattribution

Change-Id: Id537a980d32a52f6ff001c785d1e26349d251870