remove React's FC type from codebase (#3527)

* WIP-packages: remove React's FC type from codebase

* remove FC from other directories

* fix build failures

* add types to required packages

packages/cli/templates/default-plugin/src/components/ExampleComponent/ExampleComponent.tsx.hbs

@@ -1,4 +1,4 @@
-import React, { FC } from 'react';
+import React from 'react';
 import { Typography, Grid } from '@material-ui/core';
 import {
   InfoCard,
@@ -11,7 +11,7 @@ import {
 } from '@backstage/core';
 import ExampleFetchComponent from '../ExampleFetchComponent';
 
-const ExampleComponent: FC<{}> = () => (
+const ExampleComponent = () => (
   <Page themeId="tool">
     <Header title="Welcome to {{ id }}!" subtitle="Optional subtitle">
       <HeaderLabel label="Owner" value="Team X" />

packages/cli/templates/default-plugin/src/components/ExampleFetchComponent/ExampleFetchComponent.tsx.hbs

@@ -1,4 +1,4 @@
-import React, { FC } from 'react';
+import React from 'react';
 import { makeStyles } from '@material-ui/core/styles';
 import { Table, TableColumn, Progress } from '@backstage/core';
 import Alert from '@material-ui/lab/Alert';
@@ -38,7 +38,7 @@ type DenseTableProps = {
   users: User[];
 };
 
-export const DenseTable: FC<DenseTableProps> = ({ users }) => {
+export const DenseTable = ({ users }: DenseTableProps) => {
   const classes = useStyles();
 
   const columns: TableColumn[] = [
@@ -73,7 +73,7 @@ export const DenseTable: FC<DenseTableProps> = ({ users }) => {
   );
 };
 
-const ExampleFetchComponent: FC<{}> = () => {
+const ExampleFetchComponent = () => {
   const { value, loading, error } = useAsync(async (): Promise<User[]> => {
     const response = await fetch('https://randomuser.me/api/?results=20');
     const data = await response.json();