WalkEncryptionTest: Use StandardCharsets.UTF_8

Change-Id: I6eb8a33be62c452c264fb0560b988144d80a41f9
Signed-off-by: David Pursehouse <david.pursehouse@gmail.com>

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

@@ -43,7 +43,7 @@
 
 package org.eclipse.jgit.transport;
 
-import static org.eclipse.jgit.transport.WalkEncryptionTest.Util.UTF_8;
+import static java.nio.charset.StandardCharsets.UTF_8;
 import static org.eclipse.jgit.transport.WalkEncryptionTest.Util.cryptoCipherListPBE;
 import static org.eclipse.jgit.transport.WalkEncryptionTest.Util.cryptoCipherListTrans;
 import static org.eclipse.jgit.transport.WalkEncryptionTest.Util.folderDelete;
@@ -77,7 +77,6 @@ import java.net.SocketTimeoutException;
 import java.net.URL;
 import java.net.URLConnection;
 import java.net.UnknownHostException;
-import java.nio.charset.Charset;
 import java.nio.file.Files;
 import java.security.GeneralSecurityException;
 import java.security.Provider;
@@ -353,8 +352,6 @@ public class WalkEncryptionTest {
 	 */
 	static class Util {
 
-		static final Charset UTF_8 = Charset.forName("UTF-8");
-
 		/**
 		 * Read UTF-8 encoded text file into string.
 		 *