fix: Removed DB_URL reference

.env.example

@@ -9,9 +9,6 @@ DB_PORT=3306
 DB_NAME=
 DB_USER=
 DB_PASS=
-# This field is optional - if not supplied, it will be built from the above fields.
-# If you need the string to be a specific format, you may override it with this field.
-DB_URL=
 
 # Security settings
 SESSION_SECRET=