Remove augur.utils.read strains

[joverlee521]

Description of proposed changes

augur.utils.read_strains has been deprecated since January 2024.
Remove it so we stop duplicating augur.io.read_strains.

Related issue(s)

Resolves #1747

Checklist

• Automated checks pass
• Check if you need to add a changelog message
• Check if you need to add tests
• Check if you need to update docs

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 73.24%. Comparing base (efaa592) to head (06a00f7).
Report is 4 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1749   +/-   ##
=======================================
  Coverage   73.23%   73.24%           
=======================================
  Files          79       79           
  Lines        8389     8384    -5     
  Branches     1709     1709           
=======================================
- Hits         6144     6141    -3     
+ Misses       1957     1955    -2     
  Partials      288      288           

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[joverlee521]

Rebased to fix merge conflicts in changelog.

[joverlee521]

Rebased to fix merge conflicts in changelog, will merge once all tests pass.