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/cocoa/private.h

@@ -221,7 +221,7 @@ public :
     virtual void                controlTextDidChange();
 
     virtual void                AdjustClippingView(wxScrollBar* horizontal, wxScrollBar* vertical) override;
-    virtual void                UseClippingView(bool clip) override;
+    virtual void                UseClippingView() override;
     virtual WXWidget            GetContainer() const override { return m_osxClipView ? m_osxClipView : m_osxView; }
 
 protected:

include/wx/osx/core/private.h

@@ -368,7 +368,7 @@ public :
     // scrolling views need a clip subview that acts as parent for native children
     // (except for the scollbars) which are children of the view itself
     virtual void        AdjustClippingView(wxScrollBar* horizontal, wxScrollBar* vertical);
-    virtual void        UseClippingView(bool clip);
+    virtual void        UseClippingView();
 
     // returns native view which acts as a parent for native children
     virtual WXWidget    GetContainer() const;

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)

include/wx/scrolwin.h

@@ -439,7 +439,7 @@ public:
         m_targetWindow = this;
 
 #ifdef __WXMAC__
-        this->MacSetClipChildren(true);
+        this->MacSetClipChildren();
 #endif
 
         // by default, we're scrollable in both directions (but if one of the