Removes deprecated postfix config

[inkarnation]

During startup postfix logs some deprecation warnings:

[16-Mar-2025 09:10:36] NOTICE: ready to handle connections
/usr/sbin/postconf: warning: /etc/postfix/main.cf: support for parameter "smtpd_tls_eecdh_grade" will be removed; instead, do not specify (leave at default)
/usr/sbin/postconf: warning: /etc/postfix/main.cf: support for parameter "smtp_use_tls" will be removed; instead, specify "smtp_tls_security_level"
/usr/sbin/postconf: warning: /etc/postfix/main.cf: support for parameter "smtpd_use_tls" will be removed; instead, specify "smtpd_tls_security_level"

This PR takes care to remove them, as both do not require an replacement or already have the proper alternatives configured.