Move dns.h include to unrealircd.h and remove it elsewhere.

Because I need c-ares prototypes in modules.h, for next commit.
[skip ci]

include/dns.h

@@ -1,7 +1,3 @@
-/* OMG... OMG! WHAT AN INCLUDE HORROR !!! */
-#include <ares.h>
-#include <ares_version.h>
-
 typedef enum {
 	DNSREQ_CLIENT = 1,
 	DNSREQ_LINKCONF = 2,

include/struct.h

@@ -43,6 +43,8 @@
 #include <openssl/x509v3.h>
 #endif
 #include <jansson.h>
+#include <ares.h>
+#include <ares_version.h>
 #include "common.h"
 #include "sys.h"
 #include <stdio.h>

include/unrealircd.h

@@ -30,6 +30,7 @@
 #include <fcntl.h>
 #include <signal.h>
 #include "h.h"
+#include "dns.h"
 #include "version.h"
 #ifdef USE_LIBCURL
  #include <curl/curl.h>