Add c03260 to _expanded_income and fix handling of c03260 haircut

[martinholmer]

This pull request adds the self-employment tax deduction from AGI, which is represented by the c03260 variable, into the _expanded_income variable. So, now c03260 is treated in the ExpandIncome function exactly the same as the portion of social security benefits not in AGI is treated.

In the course of reviewing c03260 logic, a bug became apparent: the _ALD_SelfEmploymentTax_HC parameter was not being used in the calculation of the _earned_p and _earned_s variables even though it was being used in the calculation of the _earned variable. Because the _earned_p and earned_s variables are used only in Form 2441, the effect of this bug fix was limited in scope and small in magnitude.

This pull request causes a small change in reform comparison results for one reform that completely eliminates the AGI deduction for half of the self-employment tax; all other 50+ reform comparisons are the same as before. There are no changes in unit test results or in validation test results.

@MattHJensen @feenberg @Amy-Xu @GoFroggyRun @andersonfrailey @codykallen

[codecov-io]

Current coverage is 98.48% (diff: 100%)

Merging #1032 into master will not change coverage

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