Remove libNNPDF closure tests utilities

Created by: scarlehoff

While preparing the parser for the new commondata one problem was the (very) old data used by the closure tests in libNNPDF and nnfit. This data could already not be read by n3fit and the vp-rebuild-data existed to update the data.

This PR removes vp-rebuild-data and associate utilities since with the new format they no longer make sense and spending the time to update them to convert the data into the new format seemed like a waste of time. Closure tests for nnfit will no longer be usable. This is very much a breaking change, if someone is still using them they will have to install a version of NNPDF 4.0.8 or lower, use vp-rebuild-data and convert them to the new format.

This is just a commit on top of the new commondata reader because I want to run the tests, fitbot, etc in isolation (and give a space for people to complain) but I will just merge on top of the new reader as soon as I'm more or less sure that I haven't broken anything.

The current (meaning, the one that's now in master) vp-setupfit produces closure data such that it is compatible with nnfit and then one needs an extra step to make it compatible with n3fit (which was the rebuild script). With this changes, vp-setupfit will produce closure data that is compatible only with n3fit (and only with new data).