Remove def_upstream

src/recipe/os/BSD/FreeBSD.c

@@ -27,8 +27,6 @@ os_freebsd_prelude ()
 
   chef_set_note ("2023-09-24: 以下三个USTC, NJU, Netease 均维护了 freebsd-pkg freebsd-ports\n2023-09-27: 请务必保持Nju前面有至少一个镜像，原因请查看 freebsd 的换源函数", NULL);
 
-  def_upstream (NULL);
-
   def_sources_begin()
   {&upstream,         NULL,                  DelegateToUpstream},
   {&Ustc,             "mirrors.ustc.edu.cn", DelegateToMirror},

src/recipe/os/BSD/NetBSD.c

@@ -28,8 +28,6 @@ os_netbsd_prelude ()
 
   chef_set_note ("根据 @ykla: NetBSD 默认状态下没有 pkgsrc，用户可能安装了也可能没安装", NULL);
 
-  def_upstream (NULL);
-
   def_sources_begin()
   {&upstream,         NULL,                                                  DelegateToUpstream},
   {&MirrorZ,          "https://mirrors.cernet.edu.cn/pkgsrc/packages/NetBSD/", DelegateToMirror},

src/recipe/os/BSD/OpenBSD.c

@@ -26,8 +26,6 @@ os_openbsd_prelude ()
   chef_forbid_english(this);
   chef_forbid_user_define(this);
 
-  def_upstream (NULL);
-
   def_sources_begin()
   {&upstream,         NULL,                                     DelegateToUpstream},
   {&MirrorZ,          "https://mirrors.cernet.edu.cn/OpenBSD/", DelegateToMirror},