Delete internal OutputCaptureRule

Delete our internal `OutputCaptureRule` since we not longer have any
tests using it.

spring-boot-project/spring-boot-tools/spring-boot-test-support/src/main/java/org/springframework/boot/testsupport/system/OutputCaptureRule.java

-/*
- * Copyright 2012-2019 the original author or authors.
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *      https://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
-package org.springframework.boot.testsupport.system;
-
-import java.util.ArrayList;
-import java.util.List;
-
-import org.hamcrest.Matcher;
-import org.junit.Assert;
-import org.junit.rules.TestRule;
-import org.junit.runner.Description;
-import org.junit.runners.model.Statement;
-
-import static org.hamcrest.Matchers.allOf;
-
-/**
- * Internal JUnit {@code @Rule} to capture output from System.out and System.err.
- *
- * @author Phillip Webb
- * @author Andy Wilkinson
- * @since 2.2.0
- */
-public class OutputCaptureRule implements TestRule, CapturedOutput {
-
-	private final OutputCapture delegate = new OutputCapture();
-
-	private List<Matcher<? super String>> matchers = new ArrayList<>();
-
-	@Override
-	public Statement apply(Statement base, Description description) {
-		return new Statement() {
-			@Override
-			public void evaluate() throws Throwable {
-				OutputCaptureRule.this.delegate.push();
-				try {
-					base.evaluate();
-				}
-				finally {
-					try {
-						if (!OutputCaptureRule.this.matchers.isEmpty()) {
-							String output = OutputCaptureRule.this.delegate.toString();
-							Assert.assertThat(output, allOf(OutputCaptureRule.this.matchers));
-						}
-					}
-					finally {
-						OutputCaptureRule.this.delegate.pop();
-					}
-				}
-			}
-		};
-	}
-
-	@Override
-	public String getAll() {
-		return this.delegate.getAll();
-	}
-
-	@Override
-	public String getOut() {
-		return this.delegate.getOut();
-	}
-
-	@Override
-	public String getErr() {
-		return this.delegate.getErr();
-	}
-
-	@Override
-	public String toString() {
-		return this.delegate.toString();
-	}
-
-	/**
-	 * Verify that the output is matched by the supplied {@code matcher}. Verification is
-	 * performed after the test method has executed.
-	 * @param matcher the matcher
-	 */
-	public void expect(Matcher<? super String> matcher) {
-		this.matchers.add(matcher);
-	}
-
-}