Have Flatten & InlineInstances remove their annotations

[davidbiancolin]

Compilers that run InlineInstances multiple times would attempt to re-inline modules that no longer exist. It's possible that something may depend on these annotations after they've run -- if that's the case, I can define a new output annotation to avoid this problem.

Should i add tests to check these passes remove their annotations, or is this sufficient?

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

• bug fix

API Impact

No change.

Backend Code Generation Impact

No change.

Desired Merge Strategy

Squash.

Release Notes

Have Flatten & InlineInstances remove their annotations after invocation.

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?

[ekiwi]

LGTM

[ekiwi]

@davidbiancolin Is it enough to just get this into the next release (1.5) or do you need this fix to be available in 1.4?

[davidbiancolin]

1.5 is fine by me. :)