chore(cli-integ): cleanup unnecessary AwsClients creation (#33051)

Some fixture cleanup:

- `withCdkMigrateApp` was needlessly creating its own instance of `AwsClients` instead of reusing the one created by the `withAws` fixture.

- `withMonolithicCfnIncludeCdkApp` is no longer necessary because we now have `withSpecificFixture` which can use a non default app.

This will make it easier to introduce the allocation service logic as there is now only a single place that creates `AwsClients`

### Checklist
- [X] My code adheres to the [CONTRIBUTING GUIDE](https://github.com/aws/aws-cdk/blob/main/CONTRIBUTING.md) and [DESIGN GUIDELINES](https://github.com/aws/aws-cdk/blob/main/docs/DESIGN_GUIDELINES.md)

----

*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

Author: iliapolo

packages/@aws-cdk-testing/cli-integ/lib/aws.ts

@@ -29,10 +29,6 @@ interface ClientConfig {
 }
 
 export class AwsClients {
-  public static async default(output: NodeJS.WritableStream) {
-    const region = process.env.AWS_REGION ?? process.env.AWS_DEFAULT_REGION ?? 'us-east-1';
-    return AwsClients.forRegion(region, output);
-  }
 
   public static async forRegion(region: string, output: NodeJS.WritableStream) {
     return new AwsClients(region, output);

packages/@aws-cdk-testing/cli-integ/lib/with-cdk-app.ts

@@ -99,21 +99,23 @@ export function withCdkApp(
   return withSpecificCdkApp('app', block);
 }
 
-export function withCdkMigrateApp<A extends TestContext>(language: string, block: (context: TestFixture) => Promise<void>) {
-  return async (context: A) => {
+export function withCdkMigrateApp(
+  language: string,
+  block: (context: TestFixture) => Promise<void>,
+): (context: TestContext & AwsContext & DisableBootstrapContext) => Promise<void> {
+  return async (context: TestContext & AwsContext & DisableBootstrapContext) => {
     const stackName = `cdk-migrate-${language}-integ-${context.randomString}`;
     const integTestDir = path.join(os.tmpdir(), `cdk-migrate-${language}-integ-${context.randomString}`);
 
     context.output.write(` Stack name:   ${stackName}\n`);
     context.output.write(` Test directory: ${integTestDir}\n`);
 
-    const awsClients = await AwsClients.default(context.output);
     fs.mkdirSync(integTestDir);
     const fixture = new TestFixture(
       integTestDir,
       stackName,
       context.output,
-      awsClients,
+      context.aws,
       context.randomString,
     );
 
@@ -125,7 +127,7 @@ export function withCdkMigrateApp<A extends TestContext>(language: string, block
       path.join(integTestDir, stackName),
       stackName,
       context.output,
-      awsClients,
+      context.aws,
       context.randomString,
     );
 
@@ -145,50 +147,6 @@ export function withCdkMigrateApp<A extends TestContext>(language: string, block
   };
 }
 
-export function withMonolithicCfnIncludeCdkApp<A extends TestContext>(block: (context: TestFixture) => Promise<void>) {
-  return async (context: A) => {
-    const uberPackage = process.env.UBERPACKAGE;
-    if (!uberPackage) {
-      throw new Error('The UBERPACKAGE environment variable is required for running this test!');
-    }
-
-    const randy = context.randomString;
-    const stackNamePrefix = `cdk-uber-cfn-include-${randy}`;
-    const integTestDir = path.join(os.tmpdir(), `cdk-uber-cfn-include-${randy}`);
-
-    context.output.write(` Stack prefix:   ${stackNamePrefix}\n`);
-    context.output.write(` Test directory: ${integTestDir}\n`);
-
-    const awsClients = await AwsClients.default(context.output);
-    await cloneDirectory(path.join(RESOURCES_DIR, 'cdk-apps', 'cfn-include-app'), integTestDir, context.output);
-    const fixture = new TestFixture(
-      integTestDir,
-      stackNamePrefix,
-      context.output,
-      awsClients,
-      context.randomString,
-    );
-
-    let success = true;
-    try {
-      await installNpmPackages(fixture, {
-        [uberPackage]: fixture.packages.requestedFrameworkVersion(),
-      });
-
-      await block(fixture);
-    } catch (e) {
-      success = false;
-      throw e;
-    } finally {
-      if (process.env.INTEG_NO_CLEAN) {
-        context.log(`Left test directory in '${integTestDir}' ($INTEG_NO_CLEAN)`);
-      } else {
-        await fixture.dispose(success);
-      }
-    }
-  };
-}
-
 /**
  * Default test fixture for most (all?) integ tests
  *

packages/@aws-cdk-testing/cli-integ/tests/uberpackage/uberpackage.integtest.ts

@@ -1,9 +1,9 @@
-import { integTest, withMonolithicCfnIncludeCdkApp } from '../../lib';
+import { integTest, withSpecificFixture } from '../../lib';
 
 jest.setTimeout(600_000);
 
 describe('uberpackage', () => {
-  integTest('works with cloudformation-include', withMonolithicCfnIncludeCdkApp(async (fixture) => {
+  integTest('works with cloudformation-include', withSpecificFixture('cfn-include-app', async (fixture) => {
     fixture.log('Starting test of cfn-include with monolithic CDK');
 
     await fixture.cdkSynth();