[Warnings] Fix set-but-unused variables in anisotropic.hh's setBoundary().

This removes a bunch of code which does not appear to have any effect and a comment that refers to that code.

@markus.blatt Assigning to you since you were the last one touching that piece of code. Please decide whether there was anything of value in the removed code and merge or close as you please.

@markus.blatt Can I get some reaction, please? Otherwise I'm going to merge 2017-11-27.

I cannot compile the release as I am using Debian 8.

mentioned in commit 2942f245

merged

mentioned in commit e1159aa3

mentioned in merge request !154 (merged)