Remove buildmaster
Created by: RoyStegeman
Since we now moved to the new commondata format, we no longer need the buildmaster folder. The datafiles we need to keep have been moved to the nnpdf_data folder.
The first commit simply removes the buildmaster folder The second commit removes some outdated parts from the docs
In general I noticed the docs have a lot of outdated info (mostly old pipeline) in them that we should either update or remove. That's not the point of this PR though.