Change counted_command_line to a shared_ptr

Change counted_command_line to a shared_ptr

This changes counted_command_line to be a typedef for std::shared_ptr
and removes the associated cleanups.  In the long run I believe that
cmd_list_element should also be changed to use a shared_ptr.

gdb/ChangeLog
2017-09-20  Tom Tromey  <tom@tromey.com>

	* breakpoint.c (struct counted_command_line): Remove.
	(breakpoint_commands): Update.
	(alloc_counted_command_line, incref_counted_command_line)
	(decref_counted_command_line, do_cleanup_counted_command_line)
	(make_cleanup_decref_counted_command_line): Remove.
	(breakpoint_set_commands, commands_command_1, ~bpstats, bpstats)
	(bpstat_clear_actions, bpstat_do_actions_1, watchpoint_check)
	(bpstat_stop_status, print_one_breakpoint_location, ~breakpoint)
	(save_breakpoints): Update.
	* breakpoint.h (counted_command_line): Now a typedef to
	shared_ptr.
	(struct breakpoint) <commands>: Now a counted_command_line.
	(struct bpstats) <command>: Likewise.