Remove some cleanups from the rust code

Remove some cleanups from the rust code

This removes some cleanups from the rust code, in favor of C++ objects
with destructors.

2016-11-12  Tom Tromey  <tom@tromey.com>

	* rust-exp.y (super_name): Use std::vector.
	(lex_number): Use std::string.
	(convert_params_to_types): Return std::vector.
	(convert_ast_to_type, convert_name): Update.
	* rust-lang.c (rust_get_disr_info): Use unique_xmalloc_ptr.