Drop handleCompletion from CompletionGroup

shared/src/main/scala/async/Async.scala

@@ -58,14 +58,7 @@ object Async:
   inline def current(using async: Async): Async = async
 
   def group[T](body: Async ?=> T)(using async: Async): T =
-    withNewCompletionGroup(CompletionGroup(async.group.handleCompletion).link())(body)
-
-  def withCompletionHandler[T](handler: Cancellable => Async ?=> Unit)(body: Async ?=> T)(using async: Async): T =
-    val combined = (c: Cancellable) =>
-      (async: Async) ?=>
-        handler(c)
-        async.group.handleCompletion(c)
-    withNewCompletionGroup(CompletionGroup(combined).link())(body)
+    withNewCompletionGroup(CompletionGroup().link())(body)
 
   /** Runs a body within another completion group. When the body returns, the group is cancelled and its completion
     * awaited with the `Unlinked` group.

shared/src/main/scala/async/Cancellable.scala

@@ -25,12 +25,6 @@ trait Cancellable:
   def unlink(): this.type =
     link(CompletionGroup.Unlinked)
 
-  /** Signal completion of this cancellable to its group. */
-  def signalCompletion()(using Async): this.type =
-    this.group.handleCompletion(this)
-    this.unlink()
-    this
-
 end Cancellable
 
 object Cancellable:

shared/src/main/scala/async/CompletionGroup.scala

@@ -5,10 +5,8 @@ import scala.util.Success
 
 /** A group of cancellable objects that are completed together. Cancelling the group means cancelling all its
   * uncompleted members.
-  * @param handleCompletion
-  *   a function that gets applied to every member when it is completed or cancelled
   */
-class CompletionGroup(val handleCompletion: Cancellable => Async ?=> Unit = _ => {}) extends Cancellable.Tracking:
+class CompletionGroup extends Cancellable.Tracking:
   private val members: mutable.Set[Cancellable] = mutable.Set()
   private var canceled: Boolean = false
   private var cancelWait: Option[Promise[Unit]] = None
@@ -26,7 +24,7 @@ class CompletionGroup(val handleCompletion: Cancellable => Async ?=> Unit = _ =>
     synchronized:
       if members.nonEmpty && cancelWait.isEmpty then cancelWait = Some(Promise())
     cancelWait.foreach(cWait => cWait.future.await)
-    signalCompletion()
+    unlink()
 
   /** Add given member to the members set. If the group has already been cancelled, cancels that member immediately. */
   def add(member: Cancellable): Unit =