Remove unused identity transform from anatomical derivatives

[tsalo]

Summary

The file is named sub-PNC/anat/sub-PNC_from-orig_to-T1w_mode-image_xfm.txt.

[tsalo]

Here's the relevant section of code:

qsiprep/qsiprep/workflows/anatomical/volume.py

Lines 626 to 645 in ee895af

	if num_images == 1:
	def _get_first(in_list):
	if isinstance(in_list, (list, tuple)):
	return in_list[0]
	return in_list
	n4_correct = pe.Node(n4_interface, name="n4_correct", n_procs=omp_nthreads)
	outputnode.inputs.template_transforms = [pkgr("qsiprep", "data/itkIdentityTransform.txt")]
	workflow.connect([
	(anat_conform, outputnode, [
	(('out_file', _get_first), 'template')]),
	(anat_conform, n4_correct, [
	(('out_file', _get_first), 'input_image')]),
	(n4_correct, outputnode, [('output_image', 'bias_corrected')])
	]) # fmt:skip
	return workflow

I think what we need is individual T1w/T2w image-to-combined T1w/T2w image transforms, which isn't really captured here.

[tsalo]

fMRIPrep will write out orig-to-T1w transforms if there are multiple T1ws across sessions (not sure what happens where there are multiple T1ws in a single session), but it won't write them out if there's a single T1w, so we don't need to write out the identity transform.