Case class creates an unapply method even if one is inherited in the companion object

## Minimized code

```Scala
abstract class B{
  def unapply(arg:A)={println ("Unapply from B"); true}
}

case class A()

object A extends B

A() match {case A() => println("done")}
```

## Output

```scala
done
```

## Expectation
In Scala 2.13.4, the same code would have used the unapply from B instead, and would have displayed 
```scala
Unapply from B
done
```