fix: undo temp branch fix

[joseph-sentry]

Purpose/Motivation

this fix is having a negative effect on the db

What does this PR do?

• removing the temp branch fix file
• removing all calls to the get or update branch head, and just using the branch head
• undo breaking changes to tests

[codecov-staging]

Codecov Report

All modified and coverable lines are covered by tests ✅

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[codecov-qa]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (f0f936e) 96.07% compared to head (b169076) 96.07%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #385      +/-   ##
==========================================
- Coverage   96.07%   96.07%   -0.01%     
==========================================
  Files         634      633       -1     
  Lines       16570    16552      -18     
==========================================
- Hits        15920    15902      -18     
  Misses        650      650              

Flag	Coverage Δ
unit	96.07% <100.00%> (-0.01%)	⬇️
unit-latest-uploader	96.07% <100.00%> (-0.01%)	⬇️

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[codecov-public-qa]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (f0f936e) 96.07% compared to head (b169076) 96.07%.

@@            Coverage Diff             @@
##             main     #385      +/-   ##
==========================================
- Coverage   96.07%   96.07%   -0.01%     
==========================================
  Files         634      633       -1     
  Lines       16570    16552      -18     
==========================================
- Hits        15920    15902      -18     
  Misses        650      650              

Flag	Coverage Δ
unit	96.07% <100.00%> (-0.01%)	⬇️
unit-latest-uploader	96.07% <100.00%> (-0.01%)	⬇️

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

Files	Coverage Δ
api/internal/coverage/views.py	100.00% <100.00%> (ø)
api/public/v2/branch/serializers.py	100.00% <ø> (ø)
api/shared/mixins.py	98.52% <100.00%> (-0.03%)	⬇️
graphql_api/types/branch/branch.py	100.00% <100.00%> (ø)
graphs/views.py	92.85% <100.00%> (-0.15%)	⬇️