Remove an unused config reference.
Review Request #2141 - Created April 29, 2015 and submitted
If needed in the future, it can be added back as an option.
CI passes: https://travis-ci.org/pantsbuild/pants/builds/60618883
We aren't using this setting internally either. We have Garrett coming back on board and one of the the tasks I'm putting on his plate is to re-parent this to Patrick's simple codegen baseclass.