Function is not referenced and will be removed from exp-file
The MT4 compiler likes to issue warnings whenever some components of the source code are not used. When you see this message, it means that MetaTrader decided to remove this unused portion of the code from your compiled file.
The fact that the MetaEditor labels it a warning is a misnomer. It does not impact your code in any negative way at all. It actually speeds up the file by removing unnecessary portions.