Remove some cleanups from gnu-v3-abi.c

Remove some cleanups from gnu-v3-abi.c

This removes some cleanups from gnu-v3-abi.c, by using std::vector
rather than VEC.

gdb/ChangeLog
2017-04-12  Tom Tromey  <tom@tromey.com>

	* gnu-v3-abi.c (value_and_voffset_p): Remove typedef.
	(compare_value_and_voffset): Change type.  Update.
	(compute_vtable_size): Change type of "offset_vec".
	(gnuv3_print_vtable): Use std::vector.  Remove cleanups.
	(gnuv3_get_typeid): Remove extraneous declaration.