Remove (most) occurrences of wxT() macro from the samples

Also replace wxChar* with wxString.

Closes https://github.com/wxWidgets/wxWidgets/pull/945

samples/html/zip/zip.cpp

@@ -169,7 +169,7 @@ MyFrame::MyFrame(const wxString& title, const wxPoint& pos, const wxSize& size)
 #if wxUSE_STATUSBAR
     html -> SetRelatedStatusBar(0);
 #endif // wxUSE_STATUSBAR
-    html -> LoadPage(wxT("start.htm"));
+    html -> LoadPage("start.htm");
 }