Release ipa-prop's agg.items and make alocation more careful

This saves about 316MB WPAing Firefox

	* ipa-prop.c (build_agg_jump_func_from_list,
	ipa_read_jump_function): Reserve agg.items precisely.
	* ipa-prop.h (ipa_node_params::~ipa_node_params): Release descriptors
	(ipa_edge_args::~ipa_edge_args): Release agg.items.