Do not pass a message to the check_write method

The check_write method does not use the passed message.
The parameter was needed to implement the swap.
As the swap is not supported anymore, it is safe to remove this parameter.

src/pipe.hpp

@@ -87,7 +87,7 @@ namespace zmq
 
         //  Checks whether messages can be written to the pipe. If writing
         //  the message would cause high watermark the function returns false.
-        bool check_write (msg_t *msg_);
+        bool check_write ();
 
         //  Writes a message to the underlying pipe. Returns false if the
         //  message cannot be written because high watermark was reached.