Prevent leaking environment information.

Changes the implementation of #1820 to prevent leaking other environment information into the build output.  For example after #1820 the development, test, and production environment configurations were available in the build output (even for production builds).

Since #1825 we are using the correctly generated configuration output (placed into the global `MyAppENV` variable) so the actual modules containing each environment is not needed.

This addresses the security concerns in #1750.