Fix syntax error in interface headers

Although these headers are not supposed to be compiled, it's still
better to avoid at least the obvious typos in them.

Closes https://github.com/wxWidgets/wxWidgets/pull/2140

interface/wx/propgrid/propgridpagestate.h

@@ -376,7 +376,7 @@ public:
     */
     inline unsigned int GetActualVirtualHeight() const;
 
-    unsigned int GetColumnCount() const'
+    unsigned int GetColumnCount() const;
 
     int GetColumnMinWidth( int column ) const;
 
@@ -524,4 +524,4 @@ public:
     bool DoExpand( wxPGProperty* p );
 
     void CalculateFontAndBitmapStuff( int vspacing );
-}:
+};