Remove unused variable

Author: sakthivelmanii

google-cloud-spanner/src/main/java/com/google/cloud/spanner/Value.java

@@ -50,7 +50,6 @@
 import java.time.LocalDate;
 import java.time.LocalDateTime;
 import java.time.OffsetDateTime;
-import java.time.ZoneId;
 import java.time.ZonedDateTime;
 import java.util.ArrayList;
 import java.util.Arrays;
@@ -105,8 +104,6 @@ public abstract class Value implements Serializable {
   static final com.google.protobuf.Value NULL_PROTO =
       com.google.protobuf.Value.newBuilder().setNullValue(NullValue.NULL_VALUE).build();
 
-  private static final ZoneId UTC_ZONE = ZoneId.of("UTC");
-
   /** Constant to specify a PG Numeric NaN value. */
   public static final String NAN = "NaN";