openssh-server.postinst and openssh-server.config use Perl to get
the value of options in /etc/ssh/sshd_config.
Such simple processing can be achieved also with a very similar sed
invocation.
Using sed instead of Perl reduces the number of packages required to
install openssh-server. (Perl is a candidate for removal from
essential, see https://salsa.debian.org/gioele/debian-vm-minimal-pkgs
and https://wiki.debian.org/Proposals/EssentialOnDiet.)