Remove reflective naming

[jackkoenig]

This is built on #2561 and will need to be rebased when that is merged. This PR reverts much of the logic added there (and deprecates some of it).

I'll note that while most reflective naming is gone, the reflective naming of val io in BlackBox remains. I think that should be removed as part of the deprecation/unification of BlackBox and ExtModule.

Contributor Checklist

• Did you add Scaladoc to every public function/method?
• 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

• performance improvement
• code refactoring
• code cleanup

API Impact

This may change some names in generated hardware, see warning in #2561.

Backend Code Generation Impact

This may change some names in generated hardware

Desired Merge Strategy

• Rebase

Release Notes

Remove reflective naming. In some uncommon circumstances, this may cause the names of some signals in the emitted Verilog to change. To determine if this will affect your code, please run your Chisel generator with --warn:reflective-naming (added in Chisel v3.5.4). Note that this option only works on the older version of FIRRTL, it is a no-op in Chisel 3.6.0 and newer.

Reviewer Checklist (only modified by reviewer)

• Did you add the appropriate labels?
• Did you mark the proper milestone (Bug fix: 3.4.x, [small] API extension: 3.5.x, API modification or big change: 3.6.0)?
• Did you review?
• Did you check whether all relevant Contributor checkboxes have been checked?
• Did you do one of the following when ready to merge:
  • Squash: You/ the contributor Enable auto-merge (squash), clean up the commit message, and label with Please Merge.
  • Merge: Ensure that contributor has cleaned up their commit history, then merge with Create a merge commit.

[jackkoenig]

Marked DO NOT MERGE until #2561 is merged and this can be rebased.