usb-creator-gtk: Remove and replace text about the "[host GNU/Linux distribution]"

Upstream issue merged to https://bugs.launchpad.net/ubuntu/+source/usb-creator/+bug/2036756

Screenshots are kept here as reference in the upstream issue:

usb-creator-gtk in Ubuntu 23.04

"To try or install Ubuntu...":

image

"You may now run Ubuntu...":

Ubuntu-3

usb-creator-gtk in Trisquel 11

"To try or install Trisquel...":

image

"You may now run Trisquel...":

trisquel-3

Edited by David Hedlund
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