Revert "additional cleanup"

This reverts commit 63beb57.

ntohl(3) requires <arpa/inet.h> which got removed from the !WIN32 block.

Found through #7181 failing CI
after only applying msgpack-python's patches:

https://github.com/borgbackup/borg/actions/runs/3605243326/jobs/6080079422#step:8:51
```
src/borg/algorithms/msgpack/sysdep.h:90:28: error: ‘ntohs’ was not declared in this scope
   90 | #  define _msgpack_be16(x) ntohs(x)
      |                            ^~~~~
```

Author: klemensn

src/borg/algorithms/msgpack/sysdep.h

@@ -61,6 +61,8 @@ typedef unsigned int _msgpack_atomic_counter_t;
 #endif
 #endif
 
+#else
+#include <arpa/inet.h>  /* __BYTE_ORDER */
 #endif
 
 #if !defined(__LITTLE_ENDIAN__) && !defined(__BIG_ENDIAN__)