revert some changes going from 1.19.3 to 1.20.5

There are some new features added in Go 1.20 like string.CutPrefix.
Those will have to wait to be ported until TinyGo MIN is >= 1.20.

http/server.go

@@ -526,11 +526,12 @@ const TrailerPrefix = "Trailer:"
 func (w *response) finalTrailers() Header {
 	var t Header
 	for k, vv := range w.handlerHeader {
-		if kk, found := strings.CutPrefix(k, TrailerPrefix); found {
+		// TINYGO: CutPrefix not available until 1.20
+		if strings.HasPrefix(k, TrailerPrefix) {
 			if t == nil {
 				t = make(Header)
 			}
-			t[kk] = vv
+			t[strings.TrimPrefix(k, TrailerPrefix)] = vv
 		}
 	}
 	for _, k := range w.trailers {
@@ -760,8 +761,8 @@ func (cr *connReader) handleReadError(_ error) {
 
 // may be called from multiple goroutines.
 func (cr *connReader) closeNotify() {
-	res := cr.conn.curReq.Load()
-	if res != nil && !res.didCloseNotify.Swap(true) {
+	res, _ := cr.conn.curReq.Load().(*response)
+	if res != nil && atomic.CompareAndSwapInt32(&res.didCloseNotify, 0, 1) {
 		res.closeNotifyCh <- true
 	}
 }
@@ -2674,7 +2675,6 @@ func (srv *Server) Close() error {
 	srv.inShutdown.setTrue()
 	srv.mu.Lock()
 	defer srv.mu.Unlock()
-	srv.closeDoneChanLocked()
 	err := srv.closeListenersLocked()
 
 	// Unlock srv.mu while waiting for listenerGroup.