Don't use wxWindowBase in the interface headers

This class is an implementation detail, only wxWindow is public and there are
never objects of wxWindowBase (but not wxWindow) class in wxWidgets programs.

Closes https://github.com/wxWidgets/wxWidgets/pull/279

interface/wx/cshelp.h

@@ -36,7 +36,7 @@ public:
         Although all help providers have these functions to allow making
         wxWindow::SetHelpText() work, not all of them implement the functions.
     */
-    virtual void AddHelp(wxWindowBase* window, const wxString& text);
+    virtual void AddHelp(wxWindow* window, const wxString& text);
 
     /**
         Associates the text with the given ID.
@@ -65,7 +65,7 @@ public:
         May be used to set the same help string for all Cancel buttons in
         the application, for example.
     */
-    virtual wxString GetHelp(const wxWindowBase* window) = 0;
+    virtual wxString GetHelp(const wxWindow* window) = 0;
 
     /**
         Removes the association between the window pointer and the help text.
@@ -73,7 +73,7 @@ public:
         help strings will fill up and when window pointers are reused, the
         wrong help string will be found.
     */
-    virtual void RemoveHelp(wxWindowBase* window);
+    virtual void RemoveHelp(wxWindow* window);
 
     /**
         Set the current, application-wide help provider.
@@ -90,7 +90,7 @@ public:
         Returns @true if help was shown, or @false if no help was available for
         this window.
     */
-    virtual bool ShowHelp(wxWindowBase* window);
+    virtual bool ShowHelp(wxWindow* window);
 
     /**
         This function may be overridden to show help for the window when it
@@ -110,7 +110,7 @@ public:
 
         @since 2.7.0
     */
-    virtual bool ShowHelpAtPoint(wxWindowBase* window, const wxPoint& point,
+    virtual bool ShowHelpAtPoint(wxWindow* window, const wxPoint& point,
                                  wxHelpEvent::Origin origin);
 };