Remove iterativeConeGenJets from CMSSW, Add GenJetsNoNu to RECO/AOD

Two long outstanding issues addressed in this pull request:
- Remove iterativeCone6GenJets from RECO+HLT
- Prepare switch from ak4GenJets to ak4GenJetsNoNu in RECO+AOD
Discussed at JMAR meeting:
https://indico.cern.ch/event/357182/contribution/5/material/slides/0.pdf
After a more general presentation, to discuss the change, but before the last 7_4_X pre-release, we would like to remove the ak4GenJets collection, together with the other jet collections discussed at the RECO meeting today.
https://indico.cern.ch/event/354427/session/4/contribution/8/material/slides/0.pdf

Details:
- Add ak4GenJetsNoNu and ak8GenJetsNoNu and remove iterativeCone5GenJets from RECO+AOD
- HLT jet validation use now ak4GenJets instead of iterativeCone5GenJets as truth reference.
- Remove genMetIC5GenJets, genMetCaloAndNonPrompt.
- PAT is not yet touched and ak4GenJets are kept for a pre-release cycle because it needs new RelVals before changes are possible and ak4GenJets can be dropped
Yes, it would make more sense to switch this to ak4GenJets as well. Just to be sure, I'd like to check with the tau experts.
@jpavel: It it fine to switch this to ak4GenJets?