Code clean for libcameraservice

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

For the unused function parameters which were cast by "(void)":
We have changed them to the C++17 attribute "[[maybe_unused]]".
This seems not that necessary but it avoids redundant code lines.

Test: mmm frameworks/av/services/camera/libcameraservice,
      presubmit check.

Change-Id: Ia68b78c01f8254d76be81b1ce98d2a5c3d7eea46
Signed-off-by: Jing Mike <jingyangliu@eswincomputing.com>
diff --git a/services/camera/libcameraservice/CameraService.cpp b/services/camera/libcameraservice/CameraService.cpp
index 2a04658..8bfa588 100644
--- a/services/camera/libcameraservice/CameraService.cpp
+++ b/services/camera/libcameraservice/CameraService.cpp
@@ -3714,8 +3714,7 @@
 // ----------------------------------------------------------------------------
 
 void CameraService::Client::notifyError(int32_t errorCode,
-        const CaptureResultExtras& resultExtras) {
-    (void) resultExtras;
+        [[maybe_unused]] const CaptureResultExtras& resultExtras) {
     if (mRemoteCallback != NULL) {
         int32_t api1ErrorCode = CAMERA_ERROR_RELEASED;
         if (errorCode == hardware::camera2::ICameraDeviceCallbacks::ERROR_CAMERA_DISABLED) {