Remove java.io.

[sequencer]

Contributor Checklist

• [ ] Did you add Scaladoc to every public function/method?
• [ ] Did you update the FIRRTL spec to include every new feature/behavior?
• [ ] Did you add at least one test demonstrating the PR?
• [ ] Did you delete any extraneous printlns/debugging code?
• [ ] Did you specify the type of improvement?
• [ ] Did you state the API impact?
• [ ] Did you specify the code generation impact?
• [ ] Did you request a desired merge strategy?
• [ ] Did you add text to be included in the Release Notes for this change?

Type of Improvement

API Impact

Backend Code Generation Impact

Desired Merge Strategy

Release Notes

Reviewer Checklist (only modified by reviewer)

• [ ] Did you add the appropriate labels?
• [ ] Did you mark the proper milestone (1.2.x, 1.3.0, 1.4.0) ?
• [ ] Did you review?
• [ ] Did you check whether all relevant Contributor checkboxes have been checked?
• [ ] Did you mark as Please Merge?