Edited 4/8/2015: You should report your earnings in the year the excess contribution is made. If you exceed the 2015 IRA contribution limit, you may withdraw excess contributions and earnings from your account by the due date of your tax return (including extensions). Since you have done exactly that, you are not subject to 6% tax on the excess contribution and there are no reporting requirements, for the contribution or the excess withdrawal.
For 2016 tax return, you will receive Form 1099-R from the IRA administrator reporting the excess contribution withdrawal. You will simply report the form.
Some details:
https://www.irs.gov/publications/p590a/ch01.html#en_US_2015_publink1000230873 - shows example
https://www.irs.gov/Retirement-Plans/IRA-Year-End-Reminders
