Removed old "Transformer" code
The pair of Transformer.[ch]pp files contained old code built for SPINS before parallel transformation (over MPI) was fully implemented. These classes were replaced wholesale with Parformer.[ch]pp (Parallel Transformer), but the older code remained in the repository. Removing these files should not affect any active code. It will affect certain disued test cases (subject to changing #includes), but these cases themselves need more serious maintenance to update for the "gradient object" interface.