QList: use =default for its default constructor

Change-Id: Id5270eac2464bf2d3810de18579d4dc295e98b38
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/tools/qlist.h

@@ -114,7 +114,7 @@ public:
     }
 
 public:
-    constexpr inline QList() noexcept { }
+    QList() = default;
     explicit QList(int size)
         : d(Data::allocate(size))
     {