klippy: Allow any stats producer to determine when stats are needed

Instead of using the toolhead class to determine if stats should be
reported, allow every printer object with a stats() callback to
determine if stats are needed.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

klippy/gcode.py

@@ -77,7 +77,7 @@ class GCodeParser:
         self.move_with_transform = transform.move
         self.position_with_transform = transform.get_position
     def stats(self, eventtime):
-        return "gcodein=%d" % (self.bytes_read,)
+        return False, "gcodein=%d" % (self.bytes_read,)
     def printer_state(self, state):
         if state == 'shutdown':
             if not self.is_printer_ready: