util/ra: Use util_dynarray for the adjacency list.

util/ra: Use util_dynarray for the adjacency list.

This make the code significantly more readable, I think (along with
shorter).  Also, using util_dynarray_delete_unordered() saves us a move of
the rest of the list when removing adjacency on a node.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4537>