Remove the legacy keypad and replace it with MobileKeypad (#825)

## Summary:
Previously, the KeypadSwitch component let you toggle between the new
and old keypads. Now we always use the new keypad.

Issue: https://khanacademy.atlassian.net/browse/LC-739

Test plan:

`yarn test`

Author: benchristel

Reviewers: benchristel, handeyeco

Required Reviewers:

Approved By: handeyeco

Checks: ✅ codecov/project, ✅ codecov/patch, ✅ Upload Coverage, ✅ Publish npm snapshot (ubuntu-latest, 16.x), ✅ Lint, Typecheck, Format, and Test (ubuntu-latest, 16.x), ✅ Extract i18n strings (ubuntu-latest, 16.x), ✅ Cypress (ubuntu-latest, 16.x), ✅ Jest Coverage (ubuntu-latest, 16.x), ✅ Check for .changeset entries for all changed files (ubuntu-latest, 16.x), ✅ Check builds for changes in size (ubuntu-latest, 16.x), ✅ gerald, ✅ Publish Storybook to Chromatic (ubuntu-latest, 16.x)

Pull Request URL: #825

.changeset/funny-carrots-leave.md

@@ -0,0 +1,11 @@
+---
+"@khanacademy/math-input": major
+"@khanacademy/perseus": major
+---
+
+We've removed the deprecated `useV2Keypad` prop from the MobileKeypad component.
+
+The V2 keypad is now the default, and the old keypad has been removed.
+
+Additionally, the mobile keypad no longer accepts the `keypadActive` or
+`setKeypadActive` props. It now gets those values itself from the `KeypadContext`.

packages/math-input/src/components/__tests__/integration.test.tsx

@@ -12,8 +12,8 @@ import React, {useState} from "react";
 
 import {KeypadType} from "../../enums";
 import MathInput from "../input/math-input";
+import {MobileKeypad} from "../keypad";
 import {KeypadContext, StatefulKeypadContextProvider} from "../keypad-context";
-import KeypadSwitch from "../keypad-switch";
 
 import type {KeypadConfiguration} from "../../types";
 
@@ -60,11 +60,10 @@ function KeypadWithContext() {
         <KeypadContext.Consumer>
             {({setKeypadElement}) => {
                 return (
-                    <KeypadSwitch
+                    <MobileKeypad
                         onElementMounted={setKeypadElement}
                         onDismiss={() => {}}
                         onAnalyticsEvent={async () => {}}
-                        useV2Keypad
                     />
                 );
             }}