Remove USBCore to safe space

Hi in order to free some RAM space I figured out the there is a USB core which needs a lot of space:

2980 Bytes USBDeviceClass TOTAL

I dont use USB on my project that's using a ATSAMD21G18A and would like to remove the class

How can I do that?

I guess it is the build.usb_flags in platform.txt. remove -DUSBCON.
to upload over USB you would need then activate the bootloader with a double reset

Thanks, I'll have a look.
I'm uploading over SWD ( I dont even have a USB socket on the board)