You must have that logo somewhere in your design files. What you could do is switch to the overlay layer in the PCB design editor, press "shift S" to show only the top overlay layer, then go to "Edit" -> "Select" -> "Outside Area" (shortcut E-S-O) and drag the selection tool around the board. This will select any of the top overlay that exists outside of the board. Then just hit the "delete" key and it should delete the logo. This is assuming it is made out of primitives on the top overlay layer. If it's part of a component instead then you will need to determine which one (go through your libraries) and follow the same procedure as above but in the footprint editor.