taskgroup: remove deprecated Listen and Trigger functions

Updates tests and examples.

example_test.go

@@ -33,7 +33,7 @@ func ExampleGroup() {
 	// <done>
 }
 
-func ExampleTrigger() {
+func ExampleNew_cancel() {
 	ctx, cancel := context.WithCancel(context.Background())
 	defer cancel()
 
@@ -64,7 +64,7 @@ func ExampleTrigger() {
 	// Output: task 5 failed
 }
 
-func ExampleListen() {
+func ExampleNew_listen() {
 	// The taskgroup itself will only report the first non-nil task error, but
 	// you can use an error listener used to accumulate all of them.
 	// Calls to the listener are synchronized, so we don't need a lock.

taskgroup.go

@@ -178,18 +178,6 @@ func adaptErrorFunc(ef any) errorFunc {
 	}
 }
 
-// Trigger creates an OnError callback that calls f each time a task reports an
-// error.  The resulting callback returns task errors unmodified.
-//
-// Deprecated: Pass f directly to [New] or [Group.OnError].
-func Trigger(f func()) any { return f }
-
-// Listen creates an OnError callback that reports each non-nil task error to
-// f.  The resulting callback returns task errors unmodified.
-//
-// Deprecated: Pass f directly to [New] or [Group.OnError].
-func Listen(f func(error)) any { return f }
-
 // NoError adapts f to a Task that executes f and reports a nil error.
 func NoError(f func()) Task { return func() error { f(); return nil } }
 

taskgroup_test.go

@@ -81,9 +81,9 @@ func TestCancellation(t *testing.T) {
 	defer leaktest.Check(t)()
 
 	var errs []error
-	g := taskgroup.New(taskgroup.Listen(func(err error) {
+	g := taskgroup.New(func(err error) {
 		errs = append(errs, err)
-	}))
+	})
 
 	errOther := errors.New("something is wrong")
 	ctx, cancel := context.WithCancel(context.Background())