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.cpp b/services/camera/libcameraservice/common/CameraProviderManager.cpp
index 3aab0b1..c72986d 100644
--- a/services/camera/libcameraservice/common/CameraProviderManager.cpp
+++ b/services/camera/libcameraservice/common/CameraProviderManager.cpp
@@ -1858,13 +1858,12 @@
 CameraProviderManager::ProviderInfo::ProviderInfo(
         const std::string &providerName,
         const std::string &providerInstance,
-        CameraProviderManager *manager) :
+        [[maybe_unused]] CameraProviderManager *manager) :
         mProviderName(providerName),
         mProviderInstance(providerInstance),
         mProviderTagid(generateVendorTagId(providerName)),
         mUniqueDeviceCount(0),
         mManager(manager) {
-    (void) mManager;
 }
 
 const std::string& CameraProviderManager::ProviderInfo::getType() const {