WalkEncryptionTest: get rid of Log4J dependency

Instead use SLF4J as all other code does

Change-Id: I0fee9c0aaa1d98f918f25aa11c2160d86399467e
Signed-off-by: Marc Strapetz <marc.strapetz@syntevo.com>

org.eclipse.jgit.test/tst/org/eclipse/jgit/transport/WalkEncryptionTest.java

@@ -76,7 +76,6 @@ import java.util.UUID;
 import javax.crypto.Cipher;
 import javax.crypto.SecretKeyFactory;
 
-import org.apache.log4j.Logger;
 import org.eclipse.jgit.api.Git;
 import org.eclipse.jgit.lib.StoredConfig;
 import org.eclipse.jgit.test.resources.SampleDataRepositoryTestCase;
@@ -92,6 +91,8 @@ import org.junit.runners.MethodSorters;
 import org.junit.runners.Parameterized;
 import org.junit.runners.Parameterized.Parameters;
 import org.junit.runners.Suite;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 
 import static org.eclipse.jgit.transport.WalkEncryptionTest.Util.*;
 
@@ -119,7 +120,7 @@ public class WalkEncryptionTest {
 	/**
 	 * Logger setup: ${project_loc}/tst-rsrc/log4j.properties
 	 */
-	static final Logger logger = Logger.getLogger(WalkEncryptionTest.class);
+	static final Logger logger = LoggerFactory.getLogger(WalkEncryptionTest.class);
 
 	/**
 	 * Property names used in test session.