Don't copy arrays that don't change in `normalise`

[tomwhite]

The variant arrays are not used in append (except for checking) so there is no need to copy them in the normalise step:

vczstore/vczstore/normalise.py

Lines 121 to 127 in 338dcf4

	# copy direct from vcz1
	vcz1_copy_vars = [
	var
	for var in root1.keys()
	if not var.startswith("call_") and var != "sample_id"
	]
	copy_store(vcz1, vcz2_norm, array_keys=vcz1_copy_vars)

The reason for copying them was to ensure that normalise produces a self-contained, internally-consistent vcz. But that is not a requirement, particularly if we also do #90.