Don’t automatically select a difficulty level

[AndrewKvalheim]

Checklist

• I have read the Contribution & Best practices Guide.
• My branch is up-to-date with the upstream master branch.
• The tests pass locally with my changes.
• I have added tests that prove my fix is effective or that my feature works (if appropriate).
• I have added necessary documentation (if appropriate).

Short description of what this resolves

Opening and saving the proposal form is not idempotent; when no difficulty level has yet been chosen by the submitter, the form automatically selects the first difficulty level.

• This UI behavior is easy to overlook when intending to edit only other fields, resulting inadvertent selection and miscommunication to reviewers.
• In effect this behaves as a required field, but in a subtle and surprising way. If it’s intended for this field to be required, it should be grouped with the other required fields on the first step.

Changes proposed in this pull request

Allow the field to remain unfilled.