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>
diff --git a/services/audioflinger/AudioFlinger.cpp b/services/audioflinger/AudioFlinger.cpp
index c05aac1..ba7c6b6 100644
--- a/services/audioflinger/AudioFlinger.cpp
+++ b/services/audioflinger/AudioFlinger.cpp
@@ -4585,12 +4585,9 @@
 // ----------------------------------------------------------------------------
 
 status_t AudioFlinger::onTransactWrapper(TransactionCode code,
-                                         const Parcel& data,
-                                         uint32_t flags,
+                                         [[maybe_unused]] const Parcel& data,
+                                         [[maybe_unused]] uint32_t flags,
                                          const std::function<status_t()>& delegate) {
-    (void) data;
-    (void) flags;
-
     // make sure transactions reserved to AudioPolicyManager do not come from other processes
     switch (code) {
         case TransactionCode::SET_STREAM_VOLUME: