Annotated classes receive unwanted companion object

[japgolly]

With Scala 2.12 and Macro Paradise 2.1.0, the following snippet:

package hmmm

final class anyAnnot extends scala.annotation.StaticAnnotation

object Hmmm {
  @anyAnnot class X
  val X = 123

  class Y
  val Y = 123
}

results in this compilation error:

[error] X is already defined as (compiler-generated) case class companion object X
[error]   val X = 123
[error]       ^

This issue originally raised as scala-js/scala-js#2806.