So that it matches the executable name (/usr/bin/librewolf) and the
filename used in the FAQ (librewolf.desktop)[1].
This also makes the filename consistent with the one used on other
platforms (such as on Arch Linux[2]) and with what is used by Firefox
(firefox.desktop).
Commands used to search and replace:
$ git grep -Flz start-librewolf.desktop | xargs -0 -I '{}' sh -c \
"printf '%s\n' \"\$(sed \
's/start-librewolf/librewolf/g' '{}')\" >'{}'"
[1] 1c5a673547/pages/docs/faq.md
[2] ecb7338cbe/librewolf.desktop
Fixes: https://github.com/netblue30/firejail/issues/5460
