Remove bool parameter from MacSetClipChildren()

This parameter was always "true" in the existing calls to this function
and the underlying UseClippingView() didn't support passing "false" to
it anyhow, so it seems simpler and more clear to just remove the
parameter.

It also avoids clang warnings about it being unused.

No real changes.

include/wx/osx/window.h

@@ -224,7 +224,7 @@ public:
     // returns true if children have to clipped to the content area
     // (e.g., scrolled windows)
     bool                MacClipChildren() const { return m_clipChildren ; }
-    void                MacSetClipChildren( bool clip );
+    void                MacSetClipChildren();
 
     // returns true if the grandchildren need to be clipped to the children's content area
     // (e.g., splitter windows)