prerm is in prism2-usb-firmware-installer 0.2.9+dfsg-4.
This file is a maintainer script. It is executed when installing (*inst) or removing (*rm) the package.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 | #!/bin/sh -e
HEXFILE=/lib/firmware/ru010803.hex
FWFILE=/lib/firmware/ru010803.fw
if [ "$1" = "remove" -o "$1" = "purge" ]; then
echo "Deleting downloaded firmware files"
rm -f $HEXFILE $FWFILE
fi
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