[Refactors] If-statements

[Anselmoo]

Some if-statements can be simplified according to https://www.python.org/dev/peps/pep-0008/, as shown below.

robustness_metrics/robustness_metrics/common/pipeline_builder.py

Lines 41 to 48 in bf3bde9

	else:
	if data[key].dtype not in TPU_SUPPORTED_DTYPES:
	tf.logging.warning(
	"Removing key '{}' from data dict because its dtype {} is not in "
	" the supported dtypes: {}".format(key, data[key].dtype,
	TPU_SUPPORTED_DTYPES))
	data = _get_delete_field(key)(data)
	return data

robustness_metrics/robustness_metrics/metrics/base.py

Lines 312 to 317 in bf3bde9

	if self._dataset_info:
	if self._dataset_info.appearing_classes:
	num_classes = self._dataset_info.num_classes
	all_classes = set(range(num_classes))
	appearing_classes = set(self._dataset_info.appearing_classes)
	self._classes_to_ignore = all_classes.difference(appearing_classes)