Delete USB stick partitioning after Linux boot?

I moved Linux Mint to my second USB stick, as you can see in the picture, and then booted it onto my laptop. During the boot process, the Linux operating system partitioned itself, and I can't seem to delete this partitioning. I'd like to completely clean up the USB stick so it has full storage capacity again and no one can mess with the operating system on someone else's computer, for example, if I lend them the USB stick.