update claimed as tax dependent

[jacobkagon]

PR Checklist

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PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature (requires Feature flag)
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What is the ticket # detailing the issue?

Ticket: https://www.pivotaltracker.com/n/projects/2640060/stories/188846893

A brief description of the changes

Current behavior: Primary applicants are being marked as claimed_as_tax_dependent by themselves

New behavior: Do not allow primary applicants to claim themselves as tax dependents.

Additional Context

Include any additional context that may be relevant to the peer review process.

[vkghub]

LGTM

[jayreddy519]

LGTM.