Removed references to apache commons logging (JabRef#7907)

code-howtos and build.gradle still referenced apache commons, but slf4j
should be used instead.
CleanupUrlFormatter was the only class still using it, but never
actually used the logger, so it was removed.

build.gradle

@@ -649,7 +649,6 @@ jlink {
         provides 'org.mariadb.jdbc.credential.CredentialPlugin' with 'org.mariadb.jdbc.credential.aws.AwsIamCredentialPlugin',
                 'org.mariadb.jdbc.credential.env.EnvCredentialPlugin',
                 'org.mariadb.jdbc.credential.system.PropertiesCredentialPlugin'
-        provides 'org.apache.commons.logging.LogFactory' with 'org.apache.logging.log4j.jcl.LogFactoryImpl'
         provides 'org.slf4j.spi.SLF4JServiceProvider' with 'org.apache.logging.slf4j.SLF4JServiceProvider'
         provides 'org.apache.logging.log4j.spi.Provider' with 'org.apache.logging.log4j.core.impl.Log4jProvider'
         provides 'java.security.Provider' with 'org.bouncycastle.jce.provider.BouncyCastleProvider',

docs/getting-into-the-code/code-howtos.md

@@ -124,7 +124,7 @@ JabRef uses the logging facade [SLF4j](https://www.slf4j.org/). All log messages
 * Obtaining a logger for a class:
 
   ```java
-  private static final Log LOGGER = LogFactory.getLog(<ClassName>.class);
+  private static final Logger LOGGER = LoggerFactory.getLogger(<ClassName>.class);
   ```
 
 * If the logging event is caused by an exception, please add the exception to the log message as:

src/main/java/org/jabref/logic/formatter/bibtexfields/CleanupUrlFormatter.java

@@ -8,15 +8,11 @@
 import org.jabref.logic.cleanup.Formatter;
 import org.jabref.logic.l10n.Localization;
 
-import org.apache.commons.logging.Log;
-import org.apache.commons.logging.LogFactory;
-
 /**
  * Cleanup URL link
  */
 public class CleanupUrlFormatter extends Formatter {
 
-    private static final Log LOGGER = LogFactory.getLog(CleanupUrlFormatter.class);
     // This regexp find "url=" or "to=" parameter in full link and get text after them
     private static final Pattern PATTERN_URL = Pattern.compile("(?:url|to)=([^&]*)");