Cleanup gw.h, part 1.

Gw.h contained a fair amount of obsolete function declarations,
duplicate declarations of functions declared in utils.h and
declarations of functions that conceptually are similar to those
in utils.h.

The obsolete and duplicate ones were removed and all but one of
the remaining moved to utils.h. Correspondingly the implementation
was moved from gw_utils.c to utils.c.

The one remaining function - gw_daemonize() - is not really worthy
of a file of its own, so that is to be moved to gateway.c after which
gw_utils.c can be removed.

Gw.h still contains defines that are duplicated in
maxscale/protocol/mysql.h. The ones in gw.h are to be removed. It
appears that the entire gw.h will disappear.

include/maxscale/cdefs.h

@@ -72,5 +72,6 @@
  */
 #include <stdbool.h>
 #include <stddef.h>
+#include <stdint.h>
 
 #endif