Unable to delete circle in tDocu layer in Eagle
I think it's part of the part ARDUINOR3-BPLACE, which you can select by choosing the bottom left corner of the board and clicking properties. You can fix this in a few ways. The one I would recommend is using the exp-lbrs.ulp to generate a library from the board, modifying the resultant ARDUINOR3-BPLACE library part and then replacing the same part in your design with the modified library part.