audio policy: fix default offload info when opening an output stream

There is no reason to use different values than the ones set by
AUDIO_INFO_INITIALIZER when creating an offload info struct in
SwAudioOutputDescriptor::open().

Also removed useless code added by commit d4adbdb7.

Bug: 232048775
Test: make
Change-Id: Ib7252d8ff314478e5b61421fdcf429780de313e3