Revert m_classes_vec introduction.

Revert m_classes_vec introduction.

2017-01-10  Martin Liska  <mliska@suse.cz>

	* ipa-icf.c (sem_item_optimizer::sem_item_optimizer): Remove
	usage of m_classes_vec.
	(sem_item_optimizer::~sem_item_optimizer):  Likewise.
	(sem_item_optimizer::get_group_by_hash): Likewise.
	(sem_item_optimizer::subdivide_classes_by_equality): Likewise.
	(sem_item_optimizer::subdivide_classes_by_sensitive_refs): Likewise.
	(sem_item_optimizer::verify_classes): Likewise.
	(sem_item_optimizer::process_cong_reduction): Likewise.
	(sem_item_optimizer::dump_cong_classes): Likewise.
	(sem_item_optimizer::merge_classes): Likewise.
	* ipa-icf.h (congruence_class_hash): Rename from
	congruence_class_group_hash.  Remove declaration of
	m_classes_vec.

From-SVN: r244272