Func rename: Make it clear that update_all_descriptors() does intro points.

With the new refresh_service_descriptor() function we had both
refresh_service_descriptor() and update_service_descriptor() which is basically
the same thing.

This commit renames update_service_descriptor() to
update_service_descriptor_intro_points() to make it clear it's not a generic
refresh and it's only about intro points.

Commit changes no code.