chore: delete unused experiment fields

[carolinaecalderon]

Description

Delete unused fields from the experiment table.

Test Plan

Pass existing db intg tests.
To manually test, spin up a devcluster & check that the db (psql -h localhost -p 5432 -U postgres -d postgres) does not have "git_*" or "model_packages" columns in the experiment table

Checklist

• Changes have been manually QA'd
• User-facing API changes need the "User-facing API Change" label.
• Release notes should be added as a separate file under docs/release-notes/.
  See Release Note for details.
• Licenses should be included for new code which was copied and/or modified from any external code.

Ticket

DET-10034

[netlify]

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[corban-beaird]

Looks great! 🚀

[hkang1]

I think web isn't consuming it at all as far as I can tell (did a quick repo search) so the web portion should be good to go!