All but certain, if you don't call UIWebView in your own code, there's a 3rd party library calling it.
Are you using so many third party libraries that it is difficult to know which ?
What I would first try is google with searches like:
alamofire uses UIWebView deprecated
replacing alamofire by the name of any library you use.
The article at the following URL may help you determine what framework is using UIWebView: