Use -Werror in frameworks/native/libs/vr/libbufferhubqueue

* Remove unused variable and private field.
Bug: 66996870
Test: build with WITH_TIDY=1

Change-Id: I6a1030748372912f52c6cc17116cb55dca5731fe
diff --git a/libs/vr/libbufferhubqueue/tests/Android.bp b/libs/vr/libbufferhubqueue/tests/Android.bp
index abeb719..5eba913 100644
--- a/libs/vr/libbufferhubqueue/tests/Android.bp
+++ b/libs/vr/libbufferhubqueue/tests/Android.bp
@@ -68,6 +68,8 @@
         "-DLOG_TAG=\"buffer_transport_benchmark\"",
         "-DTRACE=0",
         "-O2",
+        "-Wall",
+        "-Werror",
     ],
     name: "buffer_transport_benchmark",
     tags: ["optional"],