Drop Label_this and fix comments referring to it

Author: odersky

compiler/src/dotty/tools/dotc/core/StdNames.scala

@@ -357,7 +357,6 @@ object StdNames {
     val Flag : N                = "Flag"
     val Ident: N                = "Ident"
     val Import: N               = "Import"
-    val Label_this: N           = "Label_this"
     val Literal: N              = "Literal"
     val LiteralAnnotArg: N      = "LiteralAnnotArg"
     val Matchable: N            = "Matchable"

compiler/src/dotty/tools/dotc/transform/DropBreaks.scala

@@ -218,10 +218,10 @@ class DropBreaks extends MiniPhase:
    *
    *     return[target] arg
    *
-   *  where `target` is the `goto` return label associated with `local`.
+   *  where `target` is the `goto` return label associated with `lbl`.
    *  Adjust associated ref counts accordingly. The local refcount is increased
-   *  and the non-local refcount is decreased, since `local` the `Label_this`
-   *  binding containing `local` is dropped.
+   *  and the non-local refcount is decreased, since the `lbl` implicit argument
+   *  to `break` is dropped.
    */
   override def transformApply(tree: Apply)(using Context): Tree =
     if enclosingBoundaries == 0 then tree