Drop aFONLL support, support FFNS

[alecandido]

As soon as everyone migrated to nFONLL we should remove all the branching with aFONLL, and just support a single FONLL implementation.

E.g. the following should only keep the if branch

pineko/src/pineko/evolve.py

Lines 133 to 139 in 3f3c887

	if check.is_num_fonll(tcard["FNS"]):
	nf = tcard["NfFF"]
	operators_card["mugrid"] = [(float(np.sqrt(q2)), int(nf)) for q2 in q2_grid]
	else:
	operators_card["mugrid"] = [
	(float(np.sqrt(q2)), nf_default(q2, atlas)) for q2 in q2_grid
	]

and this should be removed

pineko/src/pineko/check.py

Lines 161 to 163 in 3f3c887

	def is_num_fonll(FNS):
	"""Check if the FNS is a num_fonll FNS."""
	return FNS in ["FONLL-FFNS", "FONLL-FFN0"]

[alecandido]

Also considered that nf_default is not really part of the stable API (no way anyone knew it, I wrote it and decided myself :P).
So, it might be dropped or become hidden (_ prepended) at some point.

[giacomomagni]

Some of these checks are actually needed also to allow for ZM-VFNS.
Right now, What is not supported is plain FFNS.