workspace prune-files: also removes remote FLocats

[bertsky]

The documentation for the prune-files command says:

Removes mets:files that point to non-existing local files

However, that's not what is implemented:

core/src/ocrd/cli/workspace.py

Lines 560 to 577 in 26a3f78

	def prune_files(ctx, file_grp, mimetype, page_id, file_id):
	"""
	Removes mets:files that point to non-existing local files
	(If any ``FILTER`` starts with ``//``, then its remainder
	will be interpreted as a regular expression.)
	"""
	workspace = Workspace(ctx.resolver, directory=ctx.directory, mets_basename=ctx.mets_basename, automatic_backup=ctx.automatic_backup)
	with pushd_popd(workspace.directory):
	for f in workspace.find_files(
	file_id=file_id,
	file_grp=file_grp,
	mimetype=mimetype,
	page_id=page_id,
	):
	try:
	if not f.local_filename or not exists(f.local_filename):
	workspace.mets.remove_file(f.ID)

So either the documentation should read…

Removes mets:files that do not point to existing local files

…or the implementation should not remove files that also have a .url.

Since we also have workspace find ... --undo-download (removing .local_filename in METS and filesystem for those entries which also have a .url – if implemented properly, i.e. fixing #1150) the former makes more sense to me, as the latter would be redundant behaviour.