Revert "Add GPIO to rigctld.c"

This reverts commit 2e50bb2583.

tests/rigctld.c

@@ -352,10 +352,6 @@ int main(int argc, char *argv[])
             {
                 ptt_type = RIG_PTT_CM108;
             }
-            else if (!strcmp(optarg, "GPIO"))
-            {
-                ptt_type = RIG_PTT_GPIO;
-            }
             else if (!strcmp(optarg, "NONE"))
             {
                 ptt_type = RIG_PTT_NONE;