In my opinion no. Do not cut any canes you may just set the plant back and your canes next year may be smaller. Thinning is usually done when groves become over crowded. If you are growing it in a 14" pot you should just upsize the pot. Bamboos especially Black bamboo need lots of room to grow as they spread very rapidly, assuming this is a runner. Just let the plant grow the way it wants to you will see bigger canes faster this way.