Remove buildmaster

[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The second commit removes some outdated parts from the docs

In general I noticed the docs have a lot of outdated info (mostly old pipeline) in them that we should either update or remove.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.

[comane]

Hi @RoyStegeman thanks for this, this looks good to me.

I just noticed that in two of the jets datasets I had re implemented
eg nnpdf_data/nnpdf_data/new_commondata/ATLAS_2JET_7TEV_R06/filter.py

there are still mentions of buildmaster. This was for the purpose of testing and has unfortunately not been removed.

In the if __name__=="__main__" of these filter files I think one should only keep the parts that generate the datasets yaml files and remove the rest.

But I guess that this could in principle be done in a separate PR and I could take care of this.

[RoyStegeman]

I was aware of that (also some of the imports of those files are broken), but as you say, those should be fixed in a different PR.

Instead of removing the references to the old commondata files it may also be an option to point the paths to the nnpdf_data/commondata folder, I'm not sure what the best thing is to do there. It's great you want to take care of that!

You may remember that during a recent CM we discussed exactly this - that the filter.py files have not been properly reviewed and many of them are or were broken. We would like to fix this, and, where possible, make files that share the same utils, take them from a single location (as has been done in #2021 for some datasets) to make future reviews easier. At the time you offered to take charge of organising/fixing those files, is that still something you're planning to do?