Remove support for wxMotif

This port hasn't been updated for ages and is not used by anybody any
longer, so remove its code to facilitate maintenance.

Also remove references to this port from the documentation and most of
the other places (VMS-specific descrip.vms files still check for it
because it's not clear how to update them all), including configure.

Regenerate the latter and rebake all makefiles.

Finally document that this port is not available any longer.

samples/html/helpview/helpview.cpp

@@ -56,10 +56,6 @@ wxIMPLEMENT_APP(MyApp);
 
 bool MyApp::OnInit()
 {
-#ifdef __WXMOTIF__
-    delete wxLog::SetActiveTarget(new wxLogStderr); // So dialog boxes aren't used
-#endif
-
     wxInitAllImageHandlers();
     wxFileSystem::AddHandler(new wxZipFSHandler);
 
@@ -78,10 +74,6 @@ bool MyApp::OnInit()
     for (int i = 1; i < argc; i++)
         help->AddBook(wxFileName(argv[i]));
 
-#ifdef __WXMOTIF__
-    delete wxLog::SetActiveTarget(new wxLogGui);
-#endif
-
     help->SetShouldPreventAppExit(true);
 
     help -> DisplayContents();