Remove redundant `#available(iOS 13, *)` and `@available(iOS 13, *)` checks#19699

mokagio merged 6 commits intotrunkwordpress-mobile/WordPress-iOS:trunkfrom

mokagio/remove-ios-13-available-straightforwardwordpress-mobile/WordPress-iOS:mokagio/remove-ios-13-available-straightforwardCopy head branch name to clipboard