Rename a 2013/cable3 screenshot file name

As the others files do not specify macOS but are still screenshots of
macOS I have removed the '_on_macosx' from the filename. Thus
2013/cable3/screenshot_win3_on_macosx.png is now screenshot_win3.png.

Makefile updated for this.

2013/cable3/.entry.json

@@ -90,7 +90,7 @@
 	    "entry_text" : "Screenshots of some applications running on macOS"
 	},
 	{
-	    "file_path" : "screenshot_win3_on_macosx.png",
+	    "file_path" : "screenshot_win3.png",
 	    "inventory_order" : 100,
 	    "OK_to_edit" : true,
 	    "display_as" : "image",