BUILD/MINOR: lua: fix a harmless build warning

Dmitry Sivachenko reported the following build warning using Clang,
though it's harmless :

  src/hlua.c:1911:13: warning: variable '_socket_info_expanded_form' is not needed
        and will not be emitted [-Wunneeded-internal-declaration]
  static char _socket_info_expanded_form[] = SOCKET_INFO_EXPANDED_FORM;
              ^
Indeed, the variable is not used except to compute a sizeof which is
taken from the string it is initialized from. It probably is a leftover
after various code refactorings. Let's get rid of it now since it's not
used anymore.

No backport is needed.
diff --git a/src/hlua.c b/src/hlua.c
index 320e729..026dd2f 100644
--- a/src/hlua.c
+++ b/src/hlua.c
@@ -1907,9 +1907,7 @@
 	return MAY_LJMP(hlua_socket_write_yield(L, 0, 0));
 }
 
-#define SOCKET_INFO_EXPANDED_FORM "[0000:0000:0000:0000:0000:0000:0000:0000]:12345"
-static char _socket_info_expanded_form[] = SOCKET_INFO_EXPANDED_FORM;
-#define SOCKET_INFO_MAX_LEN (sizeof(_socket_info_expanded_form))
+#define SOCKET_INFO_MAX_LEN sizeof("[0000:0000:0000:0000:0000:0000:0000:0000]:12345")
 __LJMP static inline int hlua_socket_info(struct lua_State *L, struct sockaddr_storage *addr)
 {
 	static char buffer[SOCKET_INFO_MAX_LEN];