chore(logback-test.xml): remove logger configuration that seems unnecessary now.

htmlunit loggers aren't used since #530 when we migrated away of integration tests on Java.

Regarding DefaultTestContextBootstrapper I'm not sure, perhaps it was related to them too as we used
Spring context for these tests. Maybe be it wasn't related but it isn't clear why we need this now.

Author: php-coder

src/test/resources/logback-test.xml

@@ -22,19 +22,4 @@
 	</root>
 	<!-- End of org/springframework/boot/logging/logback/base.xml content -->
 
-	<!-- HtmlUnit classes -->
-	<logger name="com.gargoylesoftware.htmlunit.html.InputElementFactory" level="WARN">
-		<appender-ref ref="CONSOLE" />
-	</logger>
-	<logger name="com.gargoylesoftware.htmlunit.DefaultCssErrorHandler" level="ERROR">
-		<appender-ref ref="CONSOLE" />
-	</logger>
-	<logger name="com.gargoylesoftware.htmlunit.javascript.StrictErrorReporter" level="OFF">
-		<appender-ref ref="CONSOLE" />
-	</logger>
-	
-	<logger name="org.springframework.test.context.support.DefaultTestContextBootstrapper" level="WARN">
-		<appender-ref ref="CONSOLE" />
-	</logger>
-	
 </configuration>