Change funcall_chain to be a std::vector

Change funcall_chain to be a std::vector

This simplifies the handling of funcall_chain, by changing it to be a
std::vector<int> and then fixing the users.  This allows the removal
of a cleanup.

It would be even cleaner to replace this with better logic in the
parsers; but a baby step seemed ok.

gdb/ChangeLog
2017-09-05  Tom Tromey  <tom@tromey.com>

	* parse.c (funcall_chain): Now a std::vector.
	(start_arglist, end_arglist): Simplify.
	(free_funcalls): Remove.
	(parse_exp_in_context_1): Remove cleanup.