[14_2_X backport] simplify flat mixing configuration

[vlimant]

PR description:

plain backport of #46948

maybe help in Winter25 samples configuration

FYI @DickyChant

[cmsbuild]

A new Pull Request was created by @vlimant for CMSSW_14_2_X.

It involves the following packages:

• Configuration/StandardSequences (operations)

@antoniovilela, @cmsbuild, @davidlange6, @fabiocos, @mandrenguyen, @rappoccio can you please review it and eventually sign? Thanks.
@GiacomoSguazzoni, @Martin-Grunewald, @VinInn, @VourMa, @dgulhan, @fabiocos, @felicepantaleo, @makortel, @missirol, @mmusich, @mtosi, @rovere, @sameasy, @slomeo this is something you requested to watch as well.
@antoniovilela, @mandrenguyen, @rappoccio, @sextonkennedy you are the release manager for this.

cms-bot commands are listed here

[cmsbuild]

cms-bot internal usage

[vlimant]

please test

[cmsbuild]

+1

Size: This PR adds an extra 20KB to repository
Summary: https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-e46daa/43488/summary.html
COMMIT: 93ae856
CMSSW: CMSSW_14_2_X_2024-12-16-2300/el8_amd64_gcc12
User test area: For local testing, you can use /cvmfs/cms-ci.cern.ch/week0/cms-sw/cmssw/46972/43488/install.sh to create a dev area with all the needed externals and cmssw changes.

Comparison Summary

Summary:

• No significant changes to the logs found
• Reco comparison results: 46 differences found in the comparisons
• DQMHistoTests: Total files compared: 46
• DQMHistoTests: Total histograms compared: 3483722
• DQMHistoTests: Total failures: 1895
• DQMHistoTests: Total nulls: 0
• DQMHistoTests: Total successes: 3481807
• DQMHistoTests: Total skipped: 20
• DQMHistoTests: Total Missing objects: 0
• DQMHistoSizes: Histogram memory added: 0.0 KiB( 45 files compared)
• Checked 202 log files, 172 edm output root files, 46 DQM output files
• TriggerResults: found differences in 1 / 44 workflows