Form Explainer footer overlap fix

[virginiacc]

On page load, sometimes the form explainer sticky image overlaps the footer (per GHE 1244).

Changes

• Call updateStickiness in image onload handler on initial page load as well as when navigating between "pages" in the Form Explainer

Removals

• unnecessary formExplainer.test test function

Testing

• Check out branch & run grunt
• Navigate to http://localhost:8000/owning-a-home/loan-estimate/, scroll footer in view, and reload page. Form explainer image should not overlap footer.
• Navigate to http://localhost:8000/owning-a-home in same tab and then use back button to return to /loan-estimate page. Form explainer image should not overlap footer.

Review

• @sonnakim @mthibos @higs4281

Screenshots

What you should not see: 🙀

Notes

• I've only noticed the overlap on page load/refresh, so this fix should address that scenario. Let me know if you see it elsewhere!

Checklist

• [ ] Changes are limited to a single goal (no scope creep)
• [ ] Code can be automatically merged (no conflicts)
• [ ] Code follows the standards laid out in the front end playbook
• [ ] Passes all existing automated tests
• [ ] New functions include new tests
• [ ] New functions are documented (with a description, list of inputs, and expected output)
• [ ] Placeholder code is flagged
• [ ] Visually tested in supported browsers and devices
• [ ] Project documentation has been updated (including the "Unreleased" section of the CHANGELOG)

[sonnakim]

@virginiacc I don't have the local environment set up, but I trust it's fixed!