Remove unused size argument from Array's ctor.

format.h

@@ -271,8 +271,7 @@ class Array {
   FMT_DISALLOW_COPY_AND_ASSIGN(Array);
 
  public:
-  explicit Array(std::size_t size = 0)
-    : size_(size), capacity_(SIZE), ptr_(data_) {}
+  explicit Array() : size_(0), capacity_(SIZE), ptr_(data_) {}
   ~Array() { free(); }
 
 #if FMT_USE_RVALUE_REFERENCES