Make probe_ops::get_probes fill an std::vector

Make probe_ops::get_probes fill an std::vector

This patch changes one usage of VEC to std::vector.  It is a relatively
straightforward 1:1 change.  The implementations of
sym_probe_fns::sym_get_probes return a borrowed reference to their probe
vectors, meaning that the caller should not free it.  In the new code, I
made them return a const reference to the vector.

This patch and the following one were tested by the buildbot.  I didn't
see any failures that looked related to this one.

gdb/ChangeLog:

	* probe.h (struct probe_ops) <get_probes>: Change parameter from
	vec to std::vector.
	* probe.c (parse_probes_in_pspace): Update.
	(find_probes_in_objfile): Update.
	(find_probe_by_pc): Update.
	(collect_probes): Update.
	(probe_any_get_probes): Update.
	* symfile.h (struct sym_probe_fns) <sym_get_probes> Change
	return type to reference to std::vector.
	* dtrace-probe.c (dtrace_process_dof_probe): Change parameter to
	std::vector and update.
	(dtrace_process_dof): Likewise.
	(dtrace_get_probes): Likewise.
	* elfread.c (elf_get_probes): Change return type to std::vector,
	store an std::vector in bfd_data.
	(probe_key_free): Update to std::vector.
	* stap-probe.c (handle_stap_probe): Change parameter to
	std::vector and update.
	(stap_get_probes): Likewise.
	* symfile-debug.c (debug_sym_get_probes): Change return type to
	std::vector and update.