removed mailjet secrets api key from config, revocked the key

.env.example

@@ -31,3 +31,12 @@
 # via getenv('STRIPE_SECRET_KEY'). Use a live key in production, a test key
 # (sk_test_...) everywhere else.
 # STRIPE_SECRET_KEY=
+
+# Mailjet API key/secret pair, also used as SMTP user/pass for the
+# smtp_mailjet transport (Mailjet's own convention). Kept out of config/sync
+# (mailjet.settings.yml and symfony_mailer.mailer_transport.smtp_mailjet.yml
+# both ship empty values) and injected in settings.php. mailjet.settings'
+# APItoken is NOT set here: the mailjet module generates and persists it
+# itself from this key/secret on first use.
+# MAILJET_API_KEY=
+# MAILJET_API_SECRET=