Code clean for audioflinger

Cleaning compile warnings:
1. For "variable 'XX' set but not used":
   Remove the variables which are obviously not used;
   Add "[[maybe_unused]]" to variable declaration of the ones
       which are potentially used.
2. For "unused parameter 'XX'":
   Add "[[maybe_unused]]" to the unused function parameters.

Test: mmm frameworks/av/services/audioflinger, presubmit check.

Change-Id: I6bd6fa9a57de93f5387e1ad76342f0a0b0ac28ed
Signed-off-by: Jing Mike <jingyangliu@eswincomputing.com>