Remove iterativeConeGenJets from CMSSW, Switch from GenJets to GenJetsNoNu

Two long outstanding issues addressed in this pull request:
- Remove iterativeCone6GenJets from RECO+HLT
- Switch from ak4GenJets to ak4GenJetsNoNu in RECO+AOD
Discussed at JMAR meeting and RECO meeting:
https://indico.cern.ch/event/357182/contribution/5/material/slides/0.pdf

Details:
- RECO+AOD contain ak4GenJetsNoNu and ak8GenJetsNoNu and NO iterativeCone5GenJets
- HLT jet validation use now ak4GenJetsNoNu 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 completely

Note that we plan to remove the ak4GenJets collection, together with the other jet collections discussed at the RECO meeting today, after a more general presentation, but before the last 7_4_X pre-release.
https://indico.cern.ch/event/354427/session/4/contribution/8/material/slides/0.pdf