c++: parser cleanup, remove dummy arguments

c++: parser cleanup, remove dummy arguments

Now that cp_parser_constant_expression accepts a null non_constant_p,
we can transitively remove dummy arguments in the call chain.

Running dg.exp and counting the # of is_rvalue_constant_expression calls
from cp_parser_constant_expression:
pre-r14-2800: 2,459,145
this patch  : 1,719,454

gcc/cp/ChangeLog:

	* parser.cc (cp_parser_postfix_expression): Adjust the call to
	cp_parser_braced_list.
	(cp_parser_postfix_open_square_expression): Likewise.
	(cp_parser_new_initializer): Likewise.
	(cp_parser_assignment_expression): Adjust the call to
	cp_parser_initializer_clause.
	(cp_parser_lambda_introducer): Adjust the call to cp_parser_initializer.
	(cp_parser_range_for): Adjust the call to cp_parser_braced_list.
	(cp_parser_jump_statement): Likewise.
	(cp_parser_mem_initializer): Likewise.
	(cp_parser_template_argument): Likewise.
	(cp_parser_default_argument): Adjust the call to cp_parser_initializer.
	(cp_parser_initializer): Handle null is_direct_init and non_constant_p
	arguments.
	(cp_parser_initializer_clause): Handle null non_constant_p argument.
	(cp_parser_braced_list): Likewise.
	(cp_parser_initializer_list): Likewise.
	(cp_parser_member_declaration): Adjust the call to
	cp_parser_initializer_clause and cp_parser_initializer.
	(cp_parser_yield_expression): Adjust the call to cp_parser_braced_list.
	(cp_parser_functional_cast): Likewise.
	(cp_parser_late_parse_one_default_arg): Adjust the call to
	cp_parser_initializer.
	(cp_parser_omp_for_loop_init): Likewise.
	(cp_parser_omp_declare_reduction_exprs): Likewise.