Remove taxcalc-related variable aliases

[martinholmer]

Fixes #3232.

The copilot description of the contents of this PR is severely incomplete.

🤖 Generated by Copilot at 6755528

Summary

🐛📝🧪

This pull request renames the variable earned_income_tax_credit to eitc in the policy engine codebase, to make it more consistent with other federal credit variables. It also updates the test cases, parameters, and changelog to reflect this change. This improves the readability and maintainability of the code.

A pull request was made to rename
The earned_income_tax_credit variable, what a pain!
But eitc is shorter and neater
And makes the codebase much sweeter
So the reviewers approved it with no disdain

Walkthrough

• Rename earned_income_tax_credit to eitc for consistency with other federal credits (link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link, link)

[codecov]

Codecov Report

Attention: 2 lines in your changes are missing coverage. Please review.

Comparison is base (a4b2853) 99.01% compared to head (6755528) 99.01%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3233      +/-   ##
==========================================
- Coverage   99.01%   99.01%   -0.01%     
==========================================
  Files        1803     1803              
  Lines       26616    26606      -10     
  Branches      158      158              
==========================================
- Hits        26353    26343      -10     
  Misses        225      225              
  Partials       38       38              

Files	Coverage Δ
...s/gov/irs/credits/ctc/refundable/refundable_ctc.py	100.00% <ø> (ø)
...us/variables/gov/irs/credits/earned_income/eitc.py	100.00% <100.00%> (ø)
...edit/non_refundable_american_opportunity_credit.py	100.00% <ø> (ø)
...y_credit/refundable_american_opportunity_credit.py	100.00% <ø> (ø)
...gov/irs/credits/education/education_tax_credits.py	100.00% <100.00%> (ø)
...les/gov/irs/credits/elderly_and_disabled/credit.py	100.00% <100.00%> (ø)
...v/irs/credits/income_tax_non_refundable_credits.py	100.00% <ø> (ø)
...s/gov/irs/credits/refundable_payroll_tax_credit.py	100.00% <ø> (ø)
...ables/gov/irs/credits/retirement_savings/credit.py	100.00% <100.00%> (ø)
...variables/gov/irs/tax/federal_income/income_tax.py	88.88% <100.00%> (-0.59%)	⬇️
... and 32 more

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