Remove wxCHECK_VERSION(3,1,x) guards and legacy wxinit.h macros

Since we now target wxWidgets 3.3, all wxCHECK_VERSION(3,1,N) checks
are always true. Remove the guards keeping only the true branches:

- I18N.hpp: Remove version guard around _wxGetTranslation_ctx macro
- ExtraRenderers.hpp, GUI_App.hpp: Simplify SUPPORTS_MARKUP to check
  only wxUSE_MARKUP (version check always true)
- ConfigWizard.cpp: Remove manual wxArrayInt comparison fallback
- SendSystemInfoDialog.cpp: Simplify display scaling guard to _WIN32 only
- GUI_Utils.cpp: Remove IsDark() fallback using luma approximation
- wxinit.h: Remove legacy wxEVT_BUTTON and wxEVT_HTML_LINK_CLICKED
  compat macros (these event names exist natively in wx 3.3)

src/slic3r/GUI/ConfigWizard.cpp

@@ -902,20 +902,7 @@ void PageMaterials::update_lists(int sel_type, int sel_vendor, int last_selected
 	wxArrayInt sel_printers;
 	int sel_printers_count = list_printer->GetSelections(sel_printers);
 
-    // Does our wxWidgets version support operator== for wxArrayInt ?
-#if wxCHECK_VERSION(3, 1, 1)
     if (sel_printers != sel_printers_prev) {
-#else
-    auto are_equal = [](const wxArrayInt& arr_first, const wxArrayInt& arr_second) {
-        if (arr_first.GetCount() != arr_second.GetCount())
-            return false;
-        for (size_t i = 0; i < arr_first.GetCount(); i++)
-            if (arr_first[i] != arr_second[i])
-                return false;
-        return true;
-    };
-    if (!are_equal(sel_printers, sel_printers_prev)) {
-#endif
 
         // Refresh type list
 		list_type->Clear();