chore: cleanup the last traces of experiment git fields. [MD-258]

[ioga]

Description

Unused git fields on experiment object got removed in #8639 but they were still present in protos and CLI code. Remove them.

Test Plan

N/A: removing dead code.

Commentary (optional)

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

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (ca80022) 47.59% compared to head (f6256bb) 47.59%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #8830   +/-   ##
=======================================
  Coverage   47.59%   47.59%           
=======================================
  Files        1068     1068           
  Lines      170281   170200   -81     
  Branches     2238     2240    +2     
=======================================
- Hits        81039    81002   -37     
+ Misses      89084    89040   -44     
  Partials      158      158           

Flag	Coverage Δ
backend	43.06% <ø> (-0.01%)	⬇️
harness	64.17% <100.00%> (+0.06%)	⬆️
web	42.54% <ø> (-0.02%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
harness/determined/cli/experiment.py	23.98% <100.00%> (+0.75%)	⬆️
harness/determined/common/api/bindings.py	40.39% <ø> (-0.01%)	⬇️
master/pkg/model/experiment.go	13.63% <ø> (ø)
webui/react/src/services/api-ts-sdk/api.ts	47.59% <ø> (-0.04%)	⬇️

... and 2 files with indirect coverage changes

[carolinaecalderon]

LGTM