Get into a habit of leaving the "on primary" off all your code. When the code gets released the DBA can decide if it is appropriate where the objects (tables, indexes) are supposed to be by defining which filegroup is the default. In general its the DBA and not the developer who is responsible for the file & object placement on the system and in an agile environment under pressure you try getting 20 developers environments to accept multiple file groups!

To turn the auto scripting of then is SSMS

Menu->Tools -> options-> Sql Server Object Explorer->Scripting

scroll down to "Table and view options" then find "Script File Groups" and set the option to false.