Remove all wxS() macros from samples

The use of wxS() is an optimization which can be used to avoid an
implicit conversion from narrow to wide strings, but such optimizations
are not really needed in the samples and just make their code less
readable, so remove them.

Closes https://github.com/wxWidgets/wxWidgets/pull/956

samples/widgets/listbox.cpp

@@ -295,15 +295,15 @@ void ListboxWidgetsPage::CreateContent()
 
     static const wxString listTypes[] =
     {
-        wxS("list box")
+        "list box"
 #if wxUSE_CHECKLISTBOX
-      , wxS("check list box")
+      , "check list box"
 #endif // wxUSE_CHECKLISTBOX
 #if wxUSE_REARRANGECTRL
-      , wxS("rearrange list")
+      , "rearrange list"
 #endif // wxUSE_REARRANGECTRL
     };
-    m_radioListType = new wxRadioBox(this, wxID_ANY, wxS("&List type:"),
+    m_radioListType = new wxRadioBox(this, wxID_ANY, "&List type:",
                                     wxDefaultPosition, wxDefaultSize,
                                     WXSIZEOF(listTypes), listTypes,
                                     1, wxRA_SPECIFY_COLS);