Changes to stop the mixing module mixing anything, so that it just creat...

The input file referenced is RECO, so it has already had mixing done on it.  It doesn't have the required PSimHit, PCaloHit etcetera collections to re-run the mixing, so I took out the commands to do that.  If you do that then you get an error about the EDAlias commands referring to something that doesn't exist, so I added the "del …." lines to also remove the EDAlias.
Config file runs fine in CMSSW_6_2_4, haven't checked the results other than to see if the TrackingParticle collection is in the output file.