simplify bootstrap-driver

[smuzaffar]

drop unused archs and simplify the boot strap driver generation.

[cmsbuild]

A new Pull Request was created by @smuzaffar (Malik Shahzad Muzaffar) for branch IB/CMSSW_12_1_X/master.

@cmsbuild, @smuzaffar, @iarspider, @mrodozov can you please review it and eventually sign? Thanks.
@perrotta, @dpiparo, @qliphy you are the release manager for this.
cms-bot commands are listed here

[smuzaffar]

+externals
PR tests do not make use of it. It is only used when we build bootstrap for new archs.

[cmsbuild]

This pull request is fully signed and it will be integrated in one of the next IB/CMSSW_12_1_X/master IBs after it passes the integration tests. This pull request will now be reviewed by the release team before it's merged. @perrotta, @dpiparo, @qliphy (and backports should be raised in the release meeting by the corresponding L2)

[cmsbuild]

+1

Summary: https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-2b0485/19286/summary.html
COMMIT: 8be1667
CMSSW: CMSSW_12_1_X_2021-09-30-1100/slc7_amd64_gcc900
User test area: For local testing, you can use /cvmfs/cms-ci.cern.ch/week0/cms-sw/cmsdist/7348/19286/install.sh to create a dev area with all the needed externals and cmssw changes.

The following merge commits were also included on top of IB + this PR after doing git cms-merge-topic:

• @cms-sw simplify bootstrap-driver #7348

You can see more details here:
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-2b0485/19286/git-recent-commits.json
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-2b0485/19286/git-merge-result

Comparison Summary

Summary:

• No significant changes to the logs found
• Reco comparison results: 0 differences found in the comparisons
• DQMHistoTests: Total files compared: 40
• DQMHistoTests: Total histograms compared: 3211080
• DQMHistoTests: Total failures: 0
• DQMHistoTests: Total nulls: 0
• DQMHistoTests: Total successes: 3211058
• DQMHistoTests: Total skipped: 22
• DQMHistoTests: Total Missing objects: 0
• DQMHistoSizes: Histogram memory added: 0.0 KiB( 39 files compared)
• Checked 169 log files, 37 edm output root files, 40 DQM output files
• TriggerResults: no differences found