Logs about "/sbin/getty ttyS0" are spammed on alpine images

Logs like

Apr 22 11:50:48 alpine-server daemon.info init: process '/sbin/getty -L 0 ttyS0 vt100' (pid 2516) exited. Scheduling for restart.                                        
Apr 22 11:50:49 alpine-server daemon.info init: starting pid 2517, tty '/dev/ttyS0': '/sbin/getty -L 0 ttyS0 vt100'                                                      
Apr 22 11:50:49 alpine-server auth.err getty[2517]: tcgetattr: I/O error^M

We are not the only ones, see https://gitlab.alpinelinux.org/alpine/aports/-/issues/9324 So, we can remove the alternate console entry from /etc/inittab during the build.