Remove special check for wxTextCompleterFixed

There should be no need to handle this class specially and it's supposed
to be just an implementation detail, so don't add any dependencies on it
(if it's really important to optimize for this case, the check should be
done for wxTextCompleterSimple and use wxRTTI as wxWidgets still
supports being built without standard C++ RTTI).

src/gtk/textentry.cpp

@@ -252,20 +252,6 @@ public:
 
         if ( m_completer )
         {
-            wxTextCompleterFixed* fixedCompl =
-                dynamic_cast<wxTextCompleterFixed*>(m_completer);
-
-            if ( fixedCompl )
-            {
-                wxArrayString completions;
-                fixedCompl->GetCompletions(wxEmptyString, completions);
-
-                ChangeStrings(completions);
-
-                wxDELETE(m_completer);
-                return true;
-            }
-
             DoEnableCompletion();
 
             DoUpdateCompletionModel();