Support for webtap services was deprecated in 4.0. In 4.6 the warning message was added, but the one webtap service that ships in the product was left for backward compatibility. This particular warning will always be there on load. If this warning appears for any other service, then you need to look at it before moving to 6.x.
In 6.0 webtap support has been removed.
If you don’t know what a webtap service is, and most users don’t, then you have nothing to worry about.
webtap was a special kind of service created that supported driving through multiple raw HTML pages into order to automate input into a complex web site. It was a cool idea six years ago, but was too fragile to be useful in strategic integration projects.