fixes pick_up_tip() pressig too many times

Author: andySigler

api/opentrons/instruments/pipette.py

@@ -998,8 +998,6 @@ def _do():
 
             for i in range(int(presses) - 1):
                 self.robot.move_head(z=tip_plunge, mode='relative')
-                self.robot.move_head(z=-tip_plunge - 1, mode='relative')
-                self.robot.move_head(z=tip_plunge + 1, mode='relative')
                 self.robot.move_head(z=-tip_plunge, mode='relative')
 
         _description = "Picking up tip {0}".format(