remove an unused arg in src/butil/memory/scoped_ptr.h

src/butil/memory/scoped_ptr.h

@@ -114,7 +114,7 @@ class RefCountedThreadSafeBase;
 template <class T>
 struct DefaultDeleter {
   DefaultDeleter() {}
-  template <typename U> DefaultDeleter(const DefaultDeleter<U>& other) {
+  template <typename U> DefaultDeleter(const DefaultDeleter<U>&) {
     // IMPLEMENTATION NOTE: C++11 20.7.1.1.2p2 only provides this constructor
     // if U* is implicitly convertible to T* and U is not an array type.
     //