Remove chisel3.stage.phases.DriverCompatibility

[seldridge]

Remove the private[chisel3] phases inside the DriverCompatibility object. This then deprecates the (always publicly empty) object.

Contributor Checklist

• [n/a] Did you add Scaladoc to every public function/method?
• [n/a] 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 add appropriate documentation in docs/src?
• 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

• code cleanup

API Impact

Deprecates a public object.

Backend Code Generation Impact

None.

Desired Merge Strategy

• Squash: The PR will be squashed and merged (choose this if you have no preference.

Release Notes

Reviewer Checklist (only modified by reviewer)

• Did you add the appropriate labels?
• Did you mark the proper milestone (3.2.x, 3.3.x, 3.4.0, 3.5.0) ?
• Did you review?
• Did you check whether all relevant Contributor checkboxes have been checked?
• Did you mark as Please Merge?

[jackkoenig]

Judging by the deprecation warning, I assume this is 3.4.x? There will be waivers because package private isn't true Java binary compatibility even though we consider it so from Scala.

[seldridge]

3.4.x or 3.5 is fine. If it's the latter, I'll update the deprecation warning number again.

[jackkoenig]

Is any of this code used by the stuff @sequencer recently deleted? If so then it has to be 3.5.

[seldridge]

Yeah, Driver uses this. This needs #1730. 3.5 it is.

[sequencer]

@jackkoenig When should we get this in?
before or after 3.5 released?

[jackkoenig]

Let's get it in before 3.5