FC_USE_GTS not used since before:
1162aaea88 ("Remove references to gts and ode", 2012-07-05)
GTSAlgos.h and GTSAlgos.cpp removed in:
db5c8f7db8 ("[Mesh] remove GTSAlgos", 2022-11-11)
MeshPy::coarsen() added not later than 2011 and never implemented.