Delete jetty 6.1.26 from spark package

In spark code, jetty version is 8.1.14.v20131031 (see ./pom.xml). But when building, the jetty-6.1.26 and jetty-util-6.1.26 is packaged in spark-assembly*.jar. So the version 8.1.14.v20131031 and 6.1.26 of jetty are existed in spark-assembly*.jar. I think jetty 6.1.26 is unnecessary.