Remove WTF import

Author: Stephane Landelle

api/src/main/java/org/asynchttpclient/AsyncHttpClient.java

@@ -22,7 +22,6 @@
 import org.asynchttpclient.filter.RequestFilter;
 import org.asynchttpclient.multipart.Part;
 import org.asynchttpclient.resumable.ResumableAsyncHandler;
-import org.eclipse.jetty.http.HttpContent;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;