Change name of DropEmptyCompanions from dropEmpty to dropEmptyCompanions

dropEmpty is not as clear, as it does not indicate what it drops.
Additionally makes phaseName by in sync with class name.

Author: DarkDimius

src/dotty/tools/dotc/transform/DropEmptyCompanions.scala

@@ -30,7 +30,7 @@ import dotty.tools.dotc.transform.TreeTransforms.TransformerInfo
  */
 class DropEmptyCompanions extends MiniPhaseTransform { thisTransform =>
   import ast.tpd._
-  override def phaseName = "dropEmpty"
+  override def phaseName = "dropEmptyCompanions"
   override def runsAfter: Set[Class[_ <: Phase]] = Set(classOf[Flatten])
 
   override def transformPackageDef(pdef: PackageDef)(implicit ctx: Context, info: TransformerInfo) = {