Camera NDK: don't explicit delete ACameraMetadata

To fix the warning in RefBase destructor.

Test: NDK CTS tests, and ARCore measure app.
Bug: 112775599
Change-Id: Ia448ac6d7e6c17699c16d287f65fc2826c9d7578
diff --git a/camera/ndk/impl/ACaptureRequest.h b/camera/ndk/impl/ACaptureRequest.h
index 06b2cc3..b11dafb 100644
--- a/camera/ndk/impl/ACaptureRequest.h
+++ b/camera/ndk/impl/ACaptureRequest.h
@@ -55,7 +55,7 @@
         return ACAMERA_OK;
     }
 
-    ACameraMetadata*      settings;
+    sp<ACameraMetadata>   settings;
     ACameraOutputTargets* targets;
     void*                 context;
 };