The executables build from `frustmag/CMakeLists.txt` were intended to
run the frustmag codes (for testing purposes) without the attached SVM
framework.

This was outdated (not supporting PT) and as of the previous commit,
the frustmag-test program covers all this functionality. It has, hence,
been removed.

Basic working example for generic frustrated magnetism MC simulations. First
instantiation simulates the Heisenberg model on a 1D chain.

Subdirectory contains its own CMakeLists.txt and main.cpp to compile a
standalone executable without SVM. This is intended for initial development.