Remove deprecated stuff in finiteelementmap/

There is a lot of deprecated headers and constructors in the FEM directory. We should get rid of everything that was deprecated prior to the release of PDELab 2.0.

This basically involves

• look at the source tree of PDELab 2.0 and remove everything from master that was deprecated in 2.0.
• Fix any tests / examples in PDELab and the Howto that still use the old files / constructors etc.