Remove the old multiresolution implementation

Description

The old multiresolution implementation only worked for one region and one additional resolution and only in serial. Moreover, it hasn't been worked on for over 10 years. It is removed because it is intricately linked to the lxyz and lxyz_inv arrays that are going to be changed soon.

It is planned to have a new implementation that overcomes these issues.

News snippet

Remove old multiresolution implementation

Checklist

• I have checked that my code follows the Octopus coding standards