Merge pull request #342 from tgravescs/fix_maven_protobuf

Change protobuf version for yarn alpha back to 2.4.1

The maven build for yarn-alpha uses the wrong protobuf version and hence the generated assembly jar doesn't work with Hadoop 0.23.  Removing the setting for the yarn-alpha profile since the default protobuf version is 2.4.1 at the top of the pom file.