Remove unused rubric type for iFrame (#1996)

## Summary:
The initial goal was to separate out answers from the userInput, but iFrame is a unique widget in that the answers aren't actually contained in what is sent to the scoring function. Scoring happens via the iFrame, and the scoring function is told if the user is correct, incorrect, and incomplete. Additionally, validation happens after both types of scoring, so it most likely will not be possible to have a validation function for this widget either.

Question:
Would it be useful to change what the `scoreIframe` parameter is called as it is not actually the user's input, but a summary of the results of checking the user's input? We could revert the argument back to `state` or maybe `results`, but then would we change the type name? I wonder if that would be confusing down the road, but we do have comments explaining it somewhat.

Issue: LEMS-2440

## Test plan:
- Confirm all checks pass
- Confirm widget still works as expected via a ZND (iframe tends not to be testable locally)

Author: Myranae

Reviewers: Myranae, jeremywiebe, handeyeco

Required Reviewers:

Approved By: jeremywiebe, handeyeco

Checks: ✅ Publish npm snapshot (ubuntu-latest, 20.x), ✅ Check for .changeset entries for all changed files (ubuntu-latest, 20.x), ✅ Check builds for changes in size (ubuntu-latest, 20.x), ✅ Lint, Typecheck, Format, and Test (ubuntu-latest, 20.x), ✅ Cypress (ubuntu-latest, 20.x), ⏹️  [cancelled] Publish npm snapshot (ubuntu-latest, 20.x), ⏹️  [cancelled] Check for .changeset entries for all changed files (ubuntu-latest, 20.x), ⏹️  [cancelled] Check builds for changes in size (ubuntu-latest, 20.x), ✅ Publish Storybook to Chromatic (ubuntu-latest, 20.x), ⏹️  [cancelled] Lint, Typecheck, Format, and Test (ubuntu-latest, 20.x), ⏹️  [cancelled] Cypress (ubuntu-latest, 20.x)

Pull Request URL: #1996

.changeset/proud-ghosts-learn.md

@@ -0,0 +1,5 @@
+---
+"@khanacademy/perseus": patch
+---
+
+Remove unused iframe rubric type

packages/perseus/src/validation.types.ts

@@ -97,9 +97,6 @@ export type PerseusGrapherRubric = {
 
 export type PerseusGrapherUserInput = PerseusGrapherRubric["correct"];
 
-// TODO(LEMS-2440): Can possibly be removed during 2440; only userInput used
-export type PerseusIFrameRubric = Empty;
-
 export type PerseusIFrameUserInput = {
     status: UserInputStatus;
     message: string | null;
@@ -238,7 +235,6 @@ export type Rubric =
     | PerseusGradedGroupRubric
     | PerseusGradedGroupSetRubric
     | PerseusGrapherRubric
-    | PerseusIFrameRubric
     | PerseusInputNumberRubric
     | PerseusInteractiveGraphRubric
     | PerseusLabelImageRubric

packages/perseus/src/widgets/iframe/iframe.tsx

@@ -21,7 +21,6 @@ import {scoreIframe} from "./score-iframe";
 import type {PerseusIFrameWidgetOptions} from "../../perseus-types";
 import type {WidgetExports, WidgetProps, Widget} from "../../types";
 import type {
-    PerseusIFrameRubric,
     PerseusIFrameUserInput,
     UserInputStatus,
 } from "../../validation.types";
@@ -36,7 +35,7 @@ type RenderProps = PerseusIFrameWidgetOptions & {
     height: string;
 };
 
-type Props = WidgetProps<RenderProps, PerseusIFrameRubric>;
+type Props = WidgetProps<RenderProps>;
 
 type DefaultProps = {
     status: Props["status"];