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/propgrid/propgrid.cpp

@@ -1339,9 +1339,9 @@ void FormMain::PopulateWithExamples ()
         "Should have one extra item when compared to EnumProperty 3");
 
     // Plus property value bitmap
-    pg->Append( new wxEnumProperty(wxS("EnumProperty With Bitmap"), wxS("EnumProperty 5"),
+    pg->Append( new wxEnumProperty("EnumProperty With Bitmap", "EnumProperty 5",
         soc, 280) );
-    pg->SetPropertyHelpString(wxS("EnumProperty 5"),
+    pg->SetPropertyHelpString("EnumProperty 5",
         "Should have bitmap in front of the displayed value");
     wxBitmap bmpVal = wxArtProvider::GetBitmap(wxART_REMOVABLE);
     pg->SetPropertyImage("EnumProperty 5", bmpVal);