don't install mod_php

mod_php should not be installed nor used anymore, use php-fpm instead. might as well enable http2 at the same time:

systemctl stop apache2
a2dismod php7.3
apt-get purge -y libapache2-mod-php*
a2enconf php7.3-fpm
a2dismod mpm_prefork
a2enmod mpm_event
a2enmod http2
systemctl start apache2

I suppose an optional switch --with-http2 could be used if enabling http2 is not deemed an appropriate setup to be the default yet, but the php mode should be changed.