gnu: gzochi: Add missing dependency.

* gnu/packages/game-development.scm (gzochi)[inputs]: Add GMP.
[native-inputs]: Remove label while at it.

gnu/packages/game-development.scm

@@ -380,9 +380,10 @@ PCM data.")
                       (substitute* (find-files "." "^Makefile\\.in$")
                         (("-Werror") ""))
                       #t)))))
-    (native-inputs `(("pkgconfig" ,pkg-config)))
+    (native-inputs (list pkg-config))
     (inputs (list bdb
                   glib
+                  gmp
                   guile-3.0
                   libmicrohttpd
                   ncurses