Remove -migration setting

Author: adpi2

compiler/src/dotty/tools/dotc/config/ScalaSettings.scala

@@ -27,7 +27,6 @@ class ScalaSettings extends Settings.SettingGroup {
 
   /** Other settings */
   val deprecation: Setting[Boolean] = BooleanSetting("-deprecation", "Emit warning and location for usages of deprecated APIs.") withAbbreviation "--deprecation"
-  val migration: Setting[Boolean] = BooleanSetting("-migration", "Emit warning and location for migration issues from Scala 2.") withAbbreviation "--migration"
   val encoding: Setting[String] = StringSetting("-encoding", "encoding", "Specify character encoding used by source files.", Properties.sourceEncoding) withAbbreviation "--encoding"
   val explainTypes: Setting[Boolean] = BooleanSetting("-explain-types", "Explain type errors in more detail.") withAbbreviation "--explain-types"
   val explain: Setting[Boolean] = BooleanSetting("-explain", "Explain errors in more detail.") withAbbreviation "--explain"

compiler/src/dotty/tools/dotc/reporting/Diagnostic.scala

@@ -72,9 +72,7 @@ object Diagnostic:
   class MigrationWarning(
     msg: Message,
     pos: SourcePosition
-  ) extends Warning(msg, pos) {
-    def enablingOption(using Context): Setting[Boolean] = ctx.settings.migration
-  }
+  ) extends Warning(msg, pos)
 
 class Diagnostic(
   val msg: Message,