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/device3/Camera3BufferManager.cpp b/services/camera/libcameraservice/device3/Camera3BufferManager.cpp
index a556200..2ac38d5 100644
--- a/services/camera/libcameraservice/device3/Camera3BufferManager.cpp
+++ b/services/camera/libcameraservice/device3/Camera3BufferManager.cpp
@@ -451,10 +451,9 @@
     return OK;
 }
 
-void Camera3BufferManager::dump(int fd, const Vector<String16>& args) const {
+void Camera3BufferManager::dump(int fd, [[maybe_unused]] const Vector<String16>& args) const {
     Mutex::Autolock l(mLock);
 
-    (void) args;
     String8 lines;
     lines.appendFormat("      Total stream sets: %zu\n", mStreamSetMap.size());
     for (size_t i = 0; i < mStreamSetMap.size(); i++) {