Remove the setting -Ytrace-context-creation.

It doesn't do anything on its own, because the code that takes it
into account is commented out. Since we have to uncomment it to
enable it, there is no point in also having a setting.

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

@@ -163,7 +163,6 @@ class ScalaSettings extends Settings.SettingGroup with CommonScalaSettings {
   val Ydumpclasses: Setting[String] = StringSetting("-Ydump-classes", "dir", "Dump the generated bytecode to .class files (useful for reflective compilation that utilizes in-memory classloaders).", "")
   val YstopAfter: Setting[List[String]] = PhasesSetting("-Ystop-after", "Stop after") withAbbreviation ("-stop") // backward compat
   val YstopBefore: Setting[List[String]] = PhasesSetting("-Ystop-before", "Stop before") // stop before erasure as long as we have not debugged it fully
-  val YtraceContextCreation: Setting[Boolean] = BooleanSetting("-Ytrace-context-creation", "Store stack trace of context creations.")
   val YshowSuppressedErrors: Setting[Boolean] = BooleanSetting("-Yshow-suppressed-errors", "Also show follow-on errors and warnings that are normally suppressed.")
   val YdetailedStats: Setting[Boolean] = BooleanSetting("-Ydetailed-stats", "Show detailed internal compiler stats (needs Stats.enabled to be set to true).")
   val YkindProjector: Setting[Boolean] = BooleanSetting("-Ykind-projector", "Allow `*` as wildcard to be compatible with kind projector.")

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

@@ -338,8 +338,7 @@ object Contexts {
     private var creationTrace: Array[StackTraceElement] = _
 
     private def setCreationTrace() =
-      if (this.settings.YtraceContextCreation.value)
-        creationTrace = (new Throwable).getStackTrace().take(20)
+      creationTrace = (new Throwable).getStackTrace().take(20)
 
     /** Print all enclosing context's creation stacktraces */
     def printCreationTraces() = {