S3: should return 204 on DELETE to nonexistent file

fix https://github.com/chrislusf/seaweedfs/issues/1776

weed/s3api/s3api_object_handlers.go

@@ -296,9 +296,11 @@ func (s3a *S3ApiServer) proxyToFiler(w http.ResponseWriter, r *http.Request, des
 	defer util.CloseResponse(resp)
 
 	if (resp.ContentLength == -1 || resp.StatusCode == 404) && !strings.HasSuffix(destUrl, "/") {
+		if r.Method != "DELETE" {
 			writeErrorResponse(w, s3err.ErrNoSuchKey, r.URL)
 			return
 		}
+	}
 
 	responseFn(resp, w)