chore: form: reduce legend element reset opinionated styling

[dkilgore-eightfold]

SUMMARY:

This change reduces the opinionated styles of Form legend element.

• Removes font styles
• Removes bottom horizontal border

JIRA TASK (Eightfold Employees Only):

ENG-92464

CHANGE TYPE:

• [x] Bugfix Pull Request
• [ ] Feature Pull Request

TEST COVERAGE:

• [x] Tests for this change already exist
• [ ] I have added unittests for this change

TEST PLAN:

N/A

[codesandbox-ci[bot]]

This pull request is automatically built and testable in CodeSandbox.

To see build info of the built libraries, click here or the icon next to each commit SHA.