Remove restartWithKeepAlive as it appears to be testing the container

The restartWithKeepAlive test really appears to be testing
functionality in the container, rather than our configuration of
the container. It's also not clear what role, if any, keep-alive is
playing as it's not explicitly configured in the test.

spring-boot/src/test/java/org/springframework/boot/web/servlet/server/AbstractServletWebServerFactoryTests.java

@@ -44,7 +44,6 @@ import java.util.Locale;
 import java.util.Map;
 import java.util.Map.Entry;
 import java.util.Set;
-import java.util.concurrent.TimeUnit;
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.concurrent.atomic.AtomicReference;
 import java.util.zip.GZIPInputStream;
@@ -98,13 +97,11 @@ import org.springframework.http.HttpMethod;
 import org.springframework.http.HttpStatus;
 import org.springframework.http.client.ClientHttpRequest;
 import org.springframework.http.client.ClientHttpResponse;
-import org.springframework.http.client.HttpComponentsAsyncClientHttpRequestFactory;
 import org.springframework.http.client.HttpComponentsClientHttpRequestFactory;
 import org.springframework.test.util.ReflectionTestUtils;
 import org.springframework.util.FileCopyUtils;
 import org.springframework.util.SocketUtils;
 import org.springframework.util.StreamUtils;
-import org.springframework.util.concurrent.ListenableFuture;
 
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.hamcrest.CoreMatchers.notNullValue;
@@ -200,28 +197,6 @@ public abstract class AbstractServletWebServerFactoryTests {
 				"Unexpected response on port " + port + " : " + response);
 	}
 
-	@Test
-	public void restartWithKeepAlive() throws Exception {
-		AbstractServletWebServerFactory factory = getFactory();
-		this.webServer = factory.getWebServer(exampleServletRegistration());
-		this.webServer.start();
-		HttpComponentsAsyncClientHttpRequestFactory clientHttpRequestFactory = new HttpComponentsAsyncClientHttpRequestFactory();
-		ListenableFuture<ClientHttpResponse> response1 = clientHttpRequestFactory
-				.createAsyncRequest(new URI(getLocalUrl("/hello")), HttpMethod.GET)
-				.executeAsync();
-		assertThat(response1.get(10, TimeUnit.SECONDS).getRawStatusCode()).isEqualTo(200);
-
-		this.webServer.stop();
-		this.webServer = factory.getWebServer(exampleServletRegistration());
-		this.webServer.start();
-
-		ListenableFuture<ClientHttpResponse> response2 = clientHttpRequestFactory
-				.createAsyncRequest(new URI(getLocalUrl("/hello")), HttpMethod.GET)
-				.executeAsync();
-		assertThat(response2.get(10, TimeUnit.SECONDS).getRawStatusCode()).isEqualTo(200);
-		clientHttpRequestFactory.destroy();
-	}
-
 	@Test
 	public void startServletAndFilter() throws Exception {
 		AbstractServletWebServerFactory factory = getFactory();