docs: remove references to @backstage/core

Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>

contrib/docs/tutorials/authenticate-api-requests.md

@@ -99,7 +99,7 @@ async function main() {
 ```typescript
 // packages/app/src/App.tsx from a create-app deployment
 
-import { discoveryApiRef, useApi } from '@backstage/core';
+import { discoveryApiRef, useApi } from '@backstage/core-plugin-api';
 
 // ...
 

contrib/docs/tutorials/aws-alb-aad-oidc-auth.md

@@ -51,7 +51,7 @@ The Backstage App needs a SignInPage when authentication is required.
 When using ALB authentication Backstage will only be loaded once the user has successfully authenticated; we won't need to display a SignIn page, however we will need to create a dummy SignIn component that can refresh the token.
 
 - edit `packages/app/src/App.tsx`
-- import the following two additional definitions from `@backstage/core`: `useApi`, `configApiRef`; these will be used to check whether Backstage is running locally or behind an ALB
+- import the following two additional definitions from `@backstage/core-plugin-api`: `useApi`, `configApiRef`; these will be used to check whether Backstage is running locally or behind an ALB
 - add the following definition just before the app is created (`const app = createApp`):
 
 ```ts

contrib/docs/tutorials/quickstart-app-plugin/ExampleComponent.md

@@ -5,6 +5,7 @@ ExampleComponent.tsx reference
 ```tsx
 import React from 'react';
 import { Typography, Grid } from '@material-ui/core';
+import { identityApiRef, useApi } from '@backstage/core-plugin-api';
 import {
   InfoCard,
   Header,
@@ -13,9 +14,7 @@ import {
   ContentHeader,
   HeaderLabel,
   SupportButton,
-  identityApiRef,
-  useApi,
-} from '@backstage/core';
+} from '@backstage/core-components';
 import { ExampleFetchComponent } from '../ExampleFetchComponent';
 
 export const ExampleComponent = () => {

contrib/docs/tutorials/quickstart-app-plugin/ExampleFetchComponent.md

@@ -6,13 +6,8 @@ ExampleFetchComponent.tsx reference
 import React from 'react';
 import { useAsync } from 'react-use';
 import Alert from '@material-ui/lab/Alert';
-import {
-  Table,
-  TableColumn,
-  Progress,
-  githubAuthApiRef,
-  useApi,
-} from '@backstage/core';
+import { githubAuthApiRef, useApi } from '@backstage/core-plugin-api';
+import { Table, TableColumn, Progress } from '@backstage/core-components';
 import { graphql } from '@octokit/graphql';
 
 const query = `{