fix: remove unused logger (googleapis#1228)

Author: elharo

google-http-client/src/main/java/com/google/api/client/util/store/FileDataStoreFactory.java

@@ -37,7 +37,6 @@
 import java.util.HashSet;
 import java.util.Locale;
 import java.util.Set;
-import java.util.logging.Logger;
 
 /**
  * Thread-safe file implementation of a credential store.
@@ -55,8 +54,6 @@
  */
 public class FileDataStoreFactory extends AbstractDataStoreFactory {
 
-  private static final Logger LOGGER = Logger.getLogger(FileDataStoreFactory.class.getName());
-
   private static final boolean IS_WINDOWS =
       StandardSystemProperty.OS_NAME.value().toLowerCase(Locale.ENGLISH).startsWith("windows");