Remove unused function `_check_yaml()` in `cli.py`

[yousefmoazzam]

With the reintroduction of the check command in #201:

httomo/httomo/cli.py

Lines 34 to 46 in ae5610a

	@main.command()
	@click.argument(
	"yaml_config", type=click.Path(exists=True, dir_okay=False, path_type=Path)
	)
	@click.argument(
	"in_data_file",
	type=click.Path(exists=True, dir_okay=False, path_type=Path),
	required=False, default=None,
	)
	def check(yaml_config: Path, in_data_file: Path = None):
	"""Check a YAML pipeline file for errors."""
	in_data = str(in_data_file) if isinstance(in_data_file, PurePath) else None
	return validate_yaml_config(yaml_config, in_data)

there's no need for the function _check_yaml() now:

httomo/httomo/cli.py

Lines 182 to 184 in ae5610a

	def _check_yaml(yaml_config: Path, in_data: Path):
	"""Check a YAML pipeline file for errors."""
	return validate_yaml_config(yaml_config, in_data)