remove libc/sock/if.h

libc/sock/if.h is removed because:

- it contained only IFNAMSIZ, which was also defined in
  libc/sock/struct/ifreq.h
- it was not included in any file EXCEPT libc/isystem/net/if.h, which
  also included the libc/sock/struct/ifreq.h

hence we remove this file, and move the IFNAMSIZ definition to
libc/sock/struct/ifreq.h which is included in isystem.

libc/isystem/net/if.h

@@ -1,6 +1,5 @@
 #ifndef COSMOPOLITAN_LIBC_ISYSTEM_NET_IF_H_
 #define COSMOPOLITAN_LIBC_ISYSTEM_NET_IF_H_
-#include "libc/sock/if.h"
 #include "libc/sock/struct/ifconf.h"
 #include "libc/sock/struct/ifreq.h"
 #include "libc/sysv/consts/iff.h"

libc/sock/if.h

@@ -1,6 +0,0 @@
-#ifndef COSMOPOLITAN_LIBC_SOCK_IF_H_
-#define COSMOPOLITAN_LIBC_SOCK_IF_H_
-
-#define IFNAMSIZ 16
-
-#endif /* COSMOPOLITAN_LIBC_SOCK_IF_H_ */

libc/sock/struct/ifreq.h

@@ -5,9 +5,7 @@
 COSMOPOLITAN_C_START_
 
 #define IF_NAMESIZE 16
-#ifndef IFNAMSIZ
 #define IFNAMSIZ    IF_NAMESIZE
-#endif
 
 struct ifreq {
   union {