Dear Admission Committee,
This email is to inform you that I plan to drop a few courses listed on the transcript I submitted with my application. Those were courses I plan to take in the coming semester but I have decided to not take them any more, because I have accumulated enough credits for the requirements of graduation and I wish to spend the time of my final undergraduate semester on ....
I will remove 3 courses from the course list, including .... They will not appear in the final transcript.
I hope these courses didn't play a role in your decision of admission to my application of the ... program. I can still take these courses if you believe they could serve as important preparation for my graduate study.
Thank you blah blah blah