Remove unnecessary imports of React

In React 17 this is no longer necessary just to use JSX (see
microsoft/TypeScript#41882 (comment)).

client/src/components/App.test.tsx

@@ -1,4 +1,3 @@
-import React from "react";
 import { render, screen } from "@testing-library/react";
 import App from "components/App";
 

client/src/components/App.tsx

@@ -1,4 +1,3 @@
-import React from "react";
 import { BrowserRouter as Router, Switch, Route } from "react-router-dom";
 import { QueryClient, QueryClientProvider } from "react-query";
 

client/src/components/Icon.tsx

@@ -1,5 +1,3 @@
-import React from "react";
-
 // All icons in this file come from Refactoring UI v1.0.2
 // (https://refactoringui.com).
 

client/src/components/TaskCard.tsx

@@ -1,4 +1,3 @@
-import React from "react";
 import cn from "classnames";
 import { Link } from "react-router-dom";
 

client/src/components/pages/Add.tsx

@@ -1,4 +1,4 @@
-import React, { useState } from "react";
+import { useState } from "react";
 import cn from "classnames";
 import { Redirect } from "react-router-dom";
 

client/src/components/pages/Edit.tsx

@@ -1,4 +1,4 @@
-import React, { useState } from "react";
+import { useState } from "react";
 import cn from "classnames";
 import { useParams, Redirect } from "react-router-dom";