[Refactor] Remove unused from tests for @rails/ujs

[tricknotes]

Motivation / Background

This Pull Request has been created because some codes are unused since the following:

• use Karma as the test runner for the UJS tests #46206

Detail

This Pull Request removes unused codes.

Additional information

nothing.

Checklist

Before submitting the PR make sure the following are checked:

• This Pull Request is related to one change. Changes that are unrelated should be opened in separate PRs.
• Commit message has a detailed description of what changed and why. If this PR fixes a related issue include it in the commit message. Ex: [Fix #issue-number]
• [-] Tests are added or updated if you fix a bug or add a feature.
• [-] CHANGELOG files are updated for the changed libraries if there is a behavior change or additional feature. Minor bug fixes and documentation changes should not be included.