(ios)Remove UIWebView useragent for cordova-ios@6.x.x

[etiennea]

Platforms affected

iOS

Motivation and Context

Will not build on cordova-ios@6.x.x due to deprecated method

Description

Removes a method not available anymore

Testing

No testing required

Checklist

• [v] I've run the tests to see all new and existing tests pass
• [v] I added automated test coverage as appropriate for this change
• [v] Commit is prefixed with (platform) if this change only applies to one platform (e.g. (android))
• [v] If this Pull Request resolves an issue, I linked to the issue in the text above (and used the correct keyword to close issues using keywords)
• [v] I've updated the documentation if necessary

[timbru31]

Thank you very much for your PR, it I’ve gone ahead and re-implemented the „method“ for WKWebView support

[elisde]

Guys, will this plugin be available as a new release version? Is it possible to use latest plugin changes right now (in package.json) with UiWebView code removed in order to avoid apple play store message: ITMS-90809: Deprecated API Usage?