Remove Duplicate Includes and the Dead GCodeSender Sources (#16249)

46 files include the same header twice at file scope, outside any #if,
66 times in all:
Model.cpp included Model.hpp twice, Utils.hpp <algorithm> and
<string_view> twice, seven GUI headers <wx/dataview.h> and
<wx/artprov.h> twice. The second include of each is removed.

GCodeSender.cpp and GCodeSender.hpp have been commented out of
libslic3r/CMakeLists.txt since 2022 and their only two includes are
commented out as well. Both files go, with the commented lines, and
the CMake entry for SLA/SupportTreeIGL.cpp, a file that no longer
exists.

src/slic3r/GUI/SelectMachine.hpp

@@ -25,7 +25,6 @@
 #include <wx/dataview.h>
 #include <wx/artprov.h>
 #include <wx/xrc/xmlres.h>
-#include <wx/dataview.h>
 #include <wx/gdicmn.h>
 #include <wx/font.h>
 #include <wx/colour.h>
@@ -38,7 +37,6 @@
 #include <wx/dialog.h>
 #include <wx/popupwin.h>
 #include <wx/spinctrl.h>
-#include <wx/artprov.h>
 #include <wx/wrapsizer.h>
 #include <wx/srchctrl.h>