Polish "Polish OutputCapture and its JUnit Jupiter extension"

See gh-17049

spring-boot-project/spring-boot-test/src/main/java/org/springframework/boot/test/system/OutputCapture.java

@@ -39,7 +39,6 @@ import org.springframework.util.ClassUtils;
  * @author Phillip Webb
  * @author Andy Wilkinson
  * @author Sam Brannen
- * @since 2.2.0
  * @see OutputCaptureExtension
  * @see OutputCaptureRule
  */
@@ -128,11 +127,7 @@ class OutputCapture implements CapturedOutput {
 
 	private String get(Predicate<Type> filter) {
 		Assert.state(!this.systemCaptures.isEmpty(),
-				"No system captures found. When using JUnit 4, ensure that you have "
-						+ "registered the OutputCaptureRule via @ClassRule or @Rule "
-						+ "and that the field is public. "
-						+ "When using JUnit Jupiter, ensure that you have registered "
-						+ "the OutputCaptureExtension via @ExtendWith.");
+				"No system captures found. Please check your output capture registration.");
 		StringBuilder builder = new StringBuilder();
 		for (SystemCapture systemCapture : this.systemCaptures) {
 			systemCapture.append(builder, filter);