Eliminate agent_expr_p; VEC -> std::vector in struct bp_target_info

Eliminate agent_expr_p; VEC -> std::vector in struct bp_target_info

After the previous patch, we end up with these two types with quite
similar, and potentially confusing names:

  typedef gdb::unique_ptr<agent_expr> agent_expr_up;

  /* Pointer to an agent_expr structure.  */
  typedef struct agent_expr *agent_expr_p;

The latter is only necessary to put agent_expr pointers in VECs.  So
just eliminate it and use std::vector instead.

gdb/ChangeLog:
2016-11-08  Pedro Alves  <palves@redhat.com>

	* ax.h (agent_expr_p): Delete.
	(DEF_VEC_P (agent_expr_p)): Delete.
	* breakpoint.c (build_target_condition_list)
	(build_target_command_list): Adjust to use of std::vector.
	(bp_location_dtor): Remove now unnecessary VEC_free calls.
	* breakpoint.h: Include <vector>.
	(struct bp_target_info) <conditions, tcommands>: Now
	std::vector's.
	* remote.c (remote_add_target_side_condition): bp_tgt->conditions
	is now a std::vector; adjust.
	(remote_add_target_side_commands, remote_insert_breakpoint):
	bp_tgt->tcommands is now a std::vector; adjust.