linux-firmware: Fix removing unlicensed firmware if compression is used

linux-firmware: Fix removing unlicensed firmware if compression is used

If FIRMWARE_COMPRESSION is set, the newly added code to remove
unlicensed firmware fails with:

| Remove unlicensed firmware: acenic/tg1.bin
| rm: cannot remove '.../work/all-oe-linux/linux-firmware/20250917/image/usr/lib/firmware/acenic/tg1.bin': No such file or directory

This is because the code does not consider that the file may be
compressed.

Fix it by factoring out the code to construct the compressed file
name suffix from do_install:append() into a python function and
also use it for the actual file names listed in REMOVE_UNLICENSED.

Signed-off-by: Zoltán Böszörményi <zboszor@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>