Stop setting org.jboss.logging.provider when using Logback

This fix for gh-1928 to address a problemw with Log4j was to set
a system property that forces JBoss Logging to use SLF4J. This has the
unwanted side-effect of crashing Glassfish. We no longer support Log4j
so gh-1928 is no longer a concern. However, you can shoot yourself in
the foot by having Logback and Log4j2 on the classpath in that
particular order, but the latter has to be without its
log4j-slf4j-impl module. At this point you don't get any warnings or
error output at startup, but JBoss Logging uses Log4j2 while
everything else uses SLF4J and Logback. As a result, any logging
that's performed through JBoss Logging is silently lost.

Given the problems caused by setting the system property, and the
contrived nature of the arrangement that's necessary to cause a
problem when the property isn't set, this commit updates
LogbackLoggingSystem so that the system property is no longer set.

Closes gh-8669

spring-boot/src/main/java/org/springframework/boot/logging/logback/LogbackLoggingSystem.java

@@ -101,7 +101,6 @@ public class LogbackLoggingSystem extends Slf4JLoggingSystem {
 		}
 		super.beforeInitialize();
 		loggerContext.getTurboFilterList().add(FILTER);
-		configureJBossLoggingToUseSlf4j();
 	}
 
 	@Override
@@ -208,10 +207,6 @@ public class LogbackLoggingSystem extends Slf4JLoggingSystem {
 		loadConfiguration(initializationContext, getSelfInitializationConfig(), null);
 	}
 
-	private void configureJBossLoggingToUseSlf4j() {
-		System.setProperty("org.jboss.logging.provider", "slf4j");
-	}
-
 	@Override
 	public List<LoggerConfiguration> getLoggerConfigurations() {
 		List<LoggerConfiguration> result = new ArrayList<>();

spring-boot/src/test/java/org/springframework/boot/logging/logback/LogbackLoggingSystemTests.java

@@ -253,12 +253,6 @@ public class LogbackLoggingSystemTests extends AbstractLoggingSystemTests {
 		assertThat(output).contains("Hello debug world");
 	}
 
-	@Test
-	public void jbossLoggingIsConfiguredToUseSlf4j() {
-		this.loggingSystem.beforeInitialize();
-		assertThat(System.getProperty("org.jboss.logging.provider")).isEqualTo("slf4j");
-	}
-
 	@Test
 	public void bridgeHandlerLifecycle() {
 		assertThat(bridgeHandlerInstalled()).isFalse();