Cannot remove alternative console from /etc/inittab

I am running a diskless installation of Alpine Linux 3.18.3 on a Raspberry Pi 3 (after an upgrade from version 3.12 using the tarball https://dl-cdn.alpinelinux.org/alpine/latest-stable/releases/aarch64/alpine-rpi-3.18.3-aarch64.tar.gz). (The issue was not present on Alpine Linux version 3.12.)

The init script (likely loaded from /media/mmcblk0p1/boot/initramfs-rpi) seems to automatically append the lines

# enable login on alternative console
ttyS0::respawn:/sbin/getty -L 0 ttyS0 vt100

to my /etc/inittab file, even though I removed or commented these lines before and saved the modified version of inittab via

lbu include /etc/inittab
lbu commit -d

to alpine.apkovl.tar.gz.

This launches a console on /dev/ttyS0 on boot. I can verify that the console is running on /dev/ttyS0 and that the port cannot be read or written by the uucp group:

alpine:~$ ps aux | grep ttyS0
 2162 root      0:00 /sbin/getty -L 0 ttyS0 vt100
alpine:~$ ls -lah /dev | grep ttyS0
crw--w----    1 root     root        4,  64 Sep 14 14:09 ttyS0

However, I need the /dev/ttyS0 serial port to communicate with a custom device, thus a system console may not run there.

Note that /etc/mdev.conf configures the serial port correctly:

ttyS[0-9]*	root:uucp 0660

How can I disable the system console on /dev/ttyS0?