Use sendmail for forgejo mailing

roles/forgejo/templates/app.ini.j2

@@ -42,13 +42,9 @@ LANDING_PAGE          = explore
 
 [mailer]
 ENABLED   = true
-;;TODO: When my mailserver is ready, set PROTOCOL to smtps
+;TODO: When my mailserver is ready, set PROTOCOL to 'sendmail'
 PROTOCOL  = dummy
-SMTP_ADDR = mail.{{ forgejo_ssh_host }}
-SMTP_PORT = 465
 FROM      = {{ forgejo_mail_user }}
-USER      = {{ forgejo_mail_user }}
-PASSWD    = {{ forgejo_mail_pass }}
 
 [service]
 REGISTER_EMAIL_CONFIRM            = false