chore: Remove public modifier to BaseSystemTest

Author: lqiu96

google-cloud-logging/src/test/java/com/google/cloud/logging/BaseSystemTest.java

@@ -44,13 +44,13 @@ public class BaseSystemTest {
   protected static Logging logging;
 
   @BeforeAll
-  public static void beforeClass() {
+  static void beforeClass() {
     RemoteLoggingHelper helper = RemoteLoggingHelper.create();
     logging = helper.getOptions().getService();
   }
 
   @AfterAll
-  public static void afterClass() throws Exception {
+  static void afterClass() throws Exception {
     logging.close();
   }