change smtp env to server env

.env.selfhost.example

@@ -13,8 +13,8 @@ NEXTAUTH_URL="http://localhost:3000"
 NEXTAUTH_SECRET=
 
 #SMTP
-NEXT_PUBLIC_SMTP_HOST=smtp.mailtrap.io  # Example SMTP host
-NEXT_PUBLIC_SMTP_USER= "unsend" # Example SMTP user
+SMTP_HOST=smtp.mailtrap.io  # Example SMTP host
+SMTP_USER= "unsend" # Example SMTP user
 
 ## Auth providers any one is required
 # Github login - required