agent_expr_up: gdb::unique_ptr -> std::unique_ptr

agent_expr_up: gdb::unique_ptr -> std::unique_ptr

Now that we require C++11, use std::unique_ptr directly.  This allows
simplifying collection_list a bit by placing unique pointers in the
vector directly, making the vector own its elements.

gdb/ChangeLog:
2016-11-09  Pedro Alves  <palves@redhat.com>

	* ax-gdb.c (agent_eval_command_one): Use std::move instead of
	gdb::move.
	* ax.h (agent_expr_up): Use std::unique_ptr instead of
	gdb::unique_ptr.
	* breakpoint.c (parse_cond_to_aexpr): Use std::move instead of
	gdb::move.
	* tracepoint.c (collection_list::collect_symbol): Likewise.
	(collection_list::~collection_list): Delete.
	(encode_actions_1): Use std::move instead of gdb::move.
	(collection_list::add_aexpr): Use std::move instead of
	unique_ptr::release.
	* tracepoint.h (collection_list) <~collection_list>: Delete
	declaration.
	<m_aexprs>: Now a vector of agent_ptr_up.