Sample rate 0 means a route-dependent rate

Remove check for primary _output_ [sic] sampling rate for fast capture.
Clean up AudioRecord handling of frame count and sample rate.
Clean up AudioTrack handling of notification period updates.
Make AudioRecord and AudioTrack more similar in order of operation, comments, and whitespace.

Bug: 25641253
Bug: 21019153
Change-Id: I24a6677945987fc39a9bf93f70357e4bc7410f98