Clean up includes for gettext

It is always enabled.

configure.ac

@@ -843,7 +843,6 @@ echo D-Bus support ......... : $dbus
 echo libnotify support ..... : $libnotify
 echo libcanberra support ... : $libcanberra
 echo Plugin interface ...... : $plugin
-echo NLS/gettext ........... : $USE_NLS
 echo IPv6 support .......... : $ipv6
 echo MS Proxy NTLM \(ISA\) ... : $have_ntlm
 echo libproxy support ...... : $libproxy

src/common/hexchat.h

@@ -21,6 +21,7 @@
 
 #include <glib.h>
 #include <glib/gstdio.h>
+#include <glib/gi18n.h>
 
 #include <time.h>			/* need time_t */
 
@@ -92,20 +93,6 @@
 #define USERNAMELEN 10
 #define HIDDEN_CHAR	8			/* invisible character for xtext */
 
-#if defined(ENABLE_NLS) && !defined(_)
-#  include <libintl.h>
-#  define _(x) gettext(x)
-#  ifdef gettext_noop
-#    define N_(String) gettext_noop (String)
-#  else
-#    define N_(String) (String)
-#  endif
-#endif
-#if !defined(_)
-#  define N_(String) (String)
-#  define _(x) (x)
-#endif
-
 struct nbexec
 {
 	int myfd;

src/fe-gtk/fe-gtk.h

@@ -28,21 +28,7 @@
 #include <sys/types.h>
 #endif
 
-#if defined(ENABLE_NLS) && !defined(_)
-#  include <libintl.h>
-#  define _(x) gettext(x)
-#  ifdef gettext_noop
-#    define N_(String) gettext_noop (String)
-#  else
-#    define N_(String) (String)
-#  endif
-#endif
-#if !defined(ENABLE_NLS) && defined(_)
-#  undef _
-#  define N_(String) (String)
-#  define _(x) (x)
-#endif
-
+#include <glib/gi18n.h>
 #include <gtk/gtk.h>
 
 #ifdef HAVE_GTK_MAC