Add wxImage::ClearAlpha().

This simple method can be used to remove alpha channel from the image.

See #10915.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@63922 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

interface/wx/image.h

@@ -1396,6 +1396,16 @@ public:
     */
     void SetAlpha(int x, int y, unsigned char alpha);
 
+    /**
+        Removes the alpha channel from the image.
+
+        This function should only be called if the image has alpha channel data,
+        use HasAlpha() to check for this.
+
+        @since 2.9.1
+    */
+    void ClearAlpha();
+
     /**
         Sets the image data without performing checks.