Remove MeshPy::coarsen() and code using GTS

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.

src/Mod/Mesh/.gitattributes

@@ -1,2 +0,0 @@
-GTSAlgos.cpp    export-ignore
-GTSAlgos.h    export-ignore

src/Mod/Mesh/App/MeshPy.xml

@@ -98,11 +98,6 @@ lines = mesh.section(mesh2, [ConnectLines=True, MinDist=0.0001])
                 </UserDocu>
             </Documentation>
         </Methode>
-        <Methode Name="coarsen">
-			<Documentation>
-				<UserDocu>Coarse the mesh</UserDocu>
-			</Documentation>
-		</Methode>
 		<Methode Name="translate">
 			<Documentation>
 				<UserDocu>Apply a translation to the mesh</UserDocu>

src/Mod/Mesh/App/MeshPyImp.cpp

@@ -593,15 +593,6 @@ PyObject* MeshPy::section(PyObject* args, PyObject* kwds)
     return Py::new_reference_to(outer);
 }
 
-PyObject* MeshPy::coarsen(PyObject* args)
-{
-    if (!PyArg_ParseTuple(args, "")) {
-        return nullptr;
-    }
-    PyErr_SetString(PyExc_NotImplementedError, "Not yet implemented");
-    return nullptr;
-}
-
 PyObject* MeshPy::translate(PyObject* args)
 {
     float x {};

src/Mod/Mesh/App/PreCompiled.h

@@ -46,9 +46,6 @@
 #include <fstream>
 #include <ios>
 
-#ifdef FC_USE_GTS
-#include <gts.h>
-#endif
 // STL
 #include <algorithm>
 #include <iomanip>

src/Mod/Mesh/Gui/PreCompiled.h

@@ -37,11 +37,6 @@
 
 #ifdef _PreComp_
 
-// Gts
-#ifdef FC_USE_GTS
-#include <gts.h>
-#endif
-
 // standard
 #include <ios>
 #include <cfloat>