Running `lint` results in errors

[SallyPerez]

When running sbt lint, the following errors result in a Compilation Failed. These errors do not show up in the CI builds. The Contributing instructions do not mention lint, only quicklint, to be run before submitting a PR so that should be updated too.

Errors:

[error] .../http4s/scalafix-internal/input/src/main/scala/fix/LiteralsSyntaxWithExistingImplicitsImportTests.scala:8:29: Unused import
[error] import org.http4s.implicits._
[error]                             ^
[error].../http4s/scalafix-internal/input/src/main/scala/fix/LiteralsSyntaxWithExistingSyntaxImportTests.scala:8:30: Unused import
[error] import org.http4s.syntax.all._
[error]                              ^
[error] No warnings can be incurred under -Xfatal-warnings.
[error] three errors found
...
[error] .../http4s/scalafix-internal/output/src/main/scala/fix/LiteralsSyntaxWithExistingImplicitsImportTests.scala:3:19: Unused import
[error] import org.http4s.Uri
[error]                   ^
[error] .../http4s/scalafix-internal/output/src/main/scala/fix/LiteralsSyntaxWithExistingSyntaxImportTests.scala:3:19: Unused import
[error] import org.http4s.Uri
[error]                   ^
...
[error] No warnings can be incurred under -Xfatal-warnings.
[error] three errors found

Possible solution steps:

• Find out what is exempting these errors in the CI that is being enforced in lint
• Adjust the lint
• Update the Contributing documentation to include running lint

[rossabaker]

For the bazillion labels that we have, I'm not sure what to put on this one. It's a real issue, but we don't have anything that covers DX.