Remove fill blanks quiz (#496)

Remove usages of the FillBlanksQuizViewController. Now fill blanks quizzes marked as an unsupported.

Author: ivan-magda

Stepic/Sources/Modules/NewStep/NewStepViewController.swift

@@ -134,8 +134,6 @@ final class NewStepViewController: UIViewController, ControllerWithStepikPlaceho
                     return SortingQuizViewController(nibName: "QuizViewController", bundle: nil)
                 case .matching:
                     return MatchingQuizViewController(nibName: "QuizViewController", bundle: nil)
-                case .fillBlanks:
-                    return FillBlanksQuizViewController(nibName: "QuizViewController", bundle: nil)
                 case .code:
                     return CodeQuizViewController(nibName: "QuizViewController", bundle: nil)
                 case .sql:

Stepic/WebStepViewController.swift

@@ -218,9 +218,6 @@ class WebStepViewController: UIViewController {
         case "matching":
             initQuizController(MatchingQuizViewController(nibName: "QuizViewController", bundle: nil))
             break
-        case "fill-blanks":
-            initQuizController(FillBlanksQuizViewController(nibName: "QuizViewController", bundle: nil))
-            break
         case "code":
             initQuizController(CodeQuizViewController(nibName: "QuizViewController", bundle: nil))
             break