T7337: Switch to OpenSSL (v2022dev2)

To follow the Apertis guidelines, which chooses OpenSSL as TLS stack, switch systemd to be build against it.

In the same line drop systemd-journal-remote and its dependency libmicrohttpd-dev since it can only be built against GnuTLS but has no value for Apertis.

This MR is based on !46 (closed)