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/Camera3FakeStream.cpp b/services/camera/libcameraservice/device3/Camera3FakeStream.cpp
index 19afd69..8c0ac71 100644
--- a/services/camera/libcameraservice/device3/Camera3FakeStream.cpp
+++ b/services/camera/libcameraservice/device3/Camera3FakeStream.cpp
@@ -67,8 +67,7 @@
     return INVALID_OPERATION;
 }
 
-void Camera3FakeStream::dump(int fd, const Vector<String16> &args) const {
-    (void) args;
+void Camera3FakeStream::dump(int fd, [[maybe_unused]] const Vector<String16> &args) const {
     String8 lines;
     lines.appendFormat("    Stream[%d]: Fake\n", mId);
     write(fd, lines.string(), lines.size());
@@ -82,9 +81,8 @@
     return OK;
 }
 
-status_t Camera3FakeStream::detachBuffer(sp<GraphicBuffer>* buffer, int* fenceFd) {
-    (void) buffer;
-    (void) fenceFd;
+status_t Camera3FakeStream::detachBuffer([[maybe_unused]] sp<GraphicBuffer>* buffer,
+                [[maybe_unused]] int* fenceFd) {
     // Do nothing
     return OK;
 }