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/common/CameraProviderManager.h b/services/camera/libcameraservice/common/CameraProviderManager.h
index e8d9a37..8d60afd 100644
--- a/services/camera/libcameraservice/common/CameraProviderManager.h
+++ b/services/camera/libcameraservice/common/CameraProviderManager.h
@@ -572,17 +572,15 @@
                     hardware::CameraInfo *info) const = 0;
             virtual bool isAPI1Compatible() const = 0;
             virtual status_t dumpState(int fd) = 0;
-            virtual status_t getCameraCharacteristics(bool overrideForPerfClass,
-                    CameraMetadata *characteristics, bool overrideToPortrait) {
-                (void) overrideForPerfClass;
-                (void) characteristics;
-                (void) overrideToPortrait;
+            virtual status_t getCameraCharacteristics(
+                    [[maybe_unused]] bool overrideForPerfClass,
+                    [[maybe_unused]] CameraMetadata *characteristics,
+                    [[maybe_unused]] bool overrideToPortrait) {
                 return INVALID_OPERATION;
             }
-            virtual status_t getPhysicalCameraCharacteristics(const std::string& physicalCameraId,
-                    CameraMetadata *characteristics) const {
-                (void) physicalCameraId;
-                (void) characteristics;
+            virtual status_t getPhysicalCameraCharacteristics(
+                    [[maybe_unused]] const std::string& physicalCameraId,
+                    [[maybe_unused]] CameraMetadata *characteristics) const {
                 return INVALID_OPERATION;
             }