I don't know why everybody is telling you that this is a problem and you should worry. In fact, I would suggest the opposite: you should be happy that your employer included duties that closely resemble the NOC with your letter. The rejections due to letters I have seen so far are either because there were no duties, or there were duties but "they did not match" the duties in the NOC description. My letter had the duties copied from the NOC as well (not all of them, but it had most of them and they were an exact copy) and the reason is because that's what my job is. The NOC describes my job. Obviously my manager looked up the NOC corresponding to my job and copied the duties, nothing wrong with that.
I would be very curious to see a rejection letter that people are claiming is due to copying the duties, what does it say: "Duties resemble NOC too much" or "Duties are not very creative". Seriously, I know you are worried and everything, but you should be happy.