cf201901 builds labeled as main

[jessemapel]

I'm not 100% up on exactly what cf201901 is supposes to be but it sounds like it should be an archive of what was previously on conda-forge and should not be under main. I am concerned about removing the gcc7 label from my environment files (as it looks like conda now defaults to gcc7) and unintentionally pulling the cf201901 builds which (I think) are not compiled with gcc7.

[ocefpaf]

We can remove to "prune" the channel and make conda solver's faster but they can live in the same main label without a problem.