HADOOP-18063. Remove unused import AbstractJavaKeyStoreProvider in Shell class. (#3846)

Signed-off-by: Akira Ajisaka <aajisaka@apache.org>

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/util/Shell.java

@@ -38,7 +38,6 @@ import java.util.concurrent.atomic.AtomicBoolean;
 import org.apache.hadoop.classification.VisibleForTesting;
 import org.apache.hadoop.classification.InterfaceAudience;
 import org.apache.hadoop.classification.InterfaceStability;
-import org.apache.hadoop.security.alias.AbstractJavaKeyStoreProvider;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;