hurd: fix definition of utsname struct

- drop the "domainname" field, as it is not actually used
- bump the length of the other fields to 1024, which is the actual size
  of the C arrays on Hurd

src/unix/hurd/mod.rs

@@ -872,12 +872,11 @@ s! {
     }
 
     pub struct utsname {
-        pub sysname: [::c_char; 65],
-        pub nodename: [::c_char; 65],
-        pub release: [::c_char; 65],
-        pub version: [::c_char; 65],
-        pub machine: [::c_char; 65],
-        pub domainname: [::c_char; 65]
+        pub sysname: [::c_char; 1024],
+        pub nodename: [::c_char; 1024],
+        pub release: [::c_char; 1024],
+        pub version: [::c_char; 1024],
+        pub machine: [::c_char; 1024],
     }
 
     pub struct rlimit64 {