[Interactive Graph] Remove legacy graph (#2228)

## Summary:
The code has been updated and released for a while, and the flags have been removed!
We can officially remove the legacy graph code.

Issue: https://khanacademy.atlassian.net/browse/LEMS-2202

## Test plan:
`yarn jest`
`yarn lint`
`yarn typecheck`

Author: nishasy

Reviewers: nishasy, catandthemachines

Required Reviewers:

Approved By: catandthemachines

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

Pull Request URL: #2228

.changeset/fast-eyes-battle.md

@@ -0,0 +1,5 @@
+---
+"@khanacademy/perseus": minor
+---
+
+[Interactive Graph] Remove legacy graph

packages/perseus/src/components.ts

@@ -1,5 +1,4 @@
 export {default as ButtonGroup} from "./components/button-group";
-export {default as Graph} from "./components/graph";
 export {default as Graphie} from "./components/graphie";
 export {default as HUD} from "./components/hud";
 export {default as Icon} from "./components/icon";