Don't Dedup modules if it would change semantics (bp #1713)

[mergify]

This is an automated backport of pull request #1713 done by Mergify

Cherry-pick of e0e6856 has failed:

On branch mergify/bp/1.3.x/pr-1713
Your branch is up to date with 'origin/1.3.x'.

You are currently cherry-picking commit e0e68568.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Unmerged paths:
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	both modified:   src/main/scala/firrtl/transforms/Dedup.scala
	both modified:   src/test/scala/firrtlTests/transforms/DedupTests.scala

no changes added to commit (use "git add" and/or "git commit -a")

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