chore: remove unused ObjectReader import

Author: Zichen1028

lib/src/main/java/com/auth0/jwt/impl/PayloadDeserializer.java

@@ -9,7 +9,6 @@
 import com.fasterxml.jackson.core.type.TypeReference;
 import com.fasterxml.jackson.databind.DeserializationContext;
 import com.fasterxml.jackson.databind.JsonNode;
-import com.fasterxml.jackson.databind.ObjectReader;
 import com.fasterxml.jackson.databind.deser.std.StdDeserializer;
 
 import java.io.IOException;