Make SMTP mailer experimental

See https://git.autonomic.zone/coop-cloud/gitea/issues/10.

compose.yml

@@ -10,7 +10,6 @@ services:
       - internal_token
       - jwt_secret
       - secret_key
-      - smtp_passwd
     environment:
       - GITEA_ALLOW_ONLY_EXTERNAL_REGISTRATION
       - GITEA_APP_NAME
@@ -24,9 +23,6 @@ services:
       - GITEA_ENABLE_NOTIFY_MAIL
       - GITEA_ENABLE_OPENID_SIGNIN
       - GITEA_ENABLE_OPENID_SIGNUP
-      - GITEA_MAILER_FROM
-      - GITEA_MAILER_HOST
-      - GITEA_MAILER_USER
       - GITEA_SSH_PORT
     volumes:
       - "git:/data"
@@ -100,9 +96,6 @@ secrets:
   secret_key:
     name: ${STACK_NAME}_secret_key_${SECRET_SECRET_KEY_VERSION}
     external: true
-  smtp_passwd:
-    name: ${STACK_NAME}_smtp_passwd_${SECRET_SMTP_PASSWORD_VERSION}
-    external: true
 volumes:
   git:
   mariadb: