remove this dumb broken metaconditions json

I remove cross_sections.json for now because it just breaks everything. For some reason the git lfs link seems to be broken. We cannot continue developing in that state. It affected Florian's and Jonathon's work and now mine too. Error message when e.g. trying git pull upstream master to synchronise upstream changes with origin master (own fork):

From ssh://gitlab.cern.ch:7999/HiggsDNA-project/HiggsDNA
 * branch            master     -> FETCH_HEAD
Downloading higgs_dna/metaconditions/cross_sections.json (1.7 KB)
Error downloading object: higgs_dna/metaconditions/cross_sections.json (16ee1ec): Smudge error: Error downloading higgs_dna/metaconditions/cross_sections.json (16ee1ec0495e911e0ac5e71f0b7d5f0a4ff4316c4999d84ed65d96084844e358): [16ee1ec0495e911e0ac5e71f0b7d5f0a4ff4316c4999d84ed65d96084844e358] Object does not exist on the server or you don't have permissions to access it: [404] Object does not exist on the server or you don't have permissions to access it

Maybe we should aim to understand this error in more detail but for now I just want to stuff it away and continue developing Sorry @tbevilac but you can still keep that file in your repo and in your local clones to do your analysis, of course. I hope it does not impact your progress but if you have any suggestion or explanation please just let us know.