Remove dead code j.math.Conversion.bigInteger2Double().
Remove dead code j.math.Conversion.bigInteger2Double().

The `BigInteger.doubleValue()` uses `parseDouble(toString())`, not
this method.

scala-js/scala-js,sjrd/scala-js,scala-js/scala-js,scala-js/scala-js,sjrd/scala-js,sjrd/scala-js