FileSystemManager.unlink

wx.downloadFile({
        url: url,
        success: (res) => {
          var savePath = wx.env.USER_DATA_PATH + '/' + this.getFileName(url);
          const fs = wx.getFileSystemManager();
          fs.saveFile({ //下载成功后保存到本地
            tempFilePath: res.tempFilePath,
            filePath: savePath,
            success(res2) {
              //获取了相册的访问权限，使用 wx.saveImageToPhotosAlbum 将图片保存到相册中
              wx.saveImageToPhotosAlbum({
                filePath: savePath,
                success: () => {
                  // 保存完成后删除本地缓存文件
                  fs.unlink({
                    filePath: savePath,
                    fail(errmsg) {
                      console.log('remove file fail:', errmsg);
                    }
                  });
                },
                fail(err) {
                }
              });
            },
            fail(err2) {
            }
          });
        },
        fail: (err) => {
          console.log('download error', err);
        }
      });