fix flash of dax dialog onboarding text (#2662)

Task/Issue URL: https://app.asana.com/0/414709148257752/1206983882892075/f
Tech Design URL:
CC:

Description:
Fix a flash of text when the onboarding loads caused by the MainVC refactoring.

DuckDuckGo/DaxOnboardingViewController.swift

@@ -69,7 +69,8 @@ class DaxOnboardingViewController: UIViewController, Onboarding {
         guard !view.isHidden else { return }
 
         daxDialogContainerHeight.constant = daxDialog?.calculateHeight() ?? 0
-
+        self.daxDialog?.reset()
+
         DispatchQueue.main.asyncAfter(deadline: .now() + Constants.animationDelay) {
             self.transitionFromOnboarding()
         }