Get rid of an unused variable.

There's no need for the capture_option_specified variable; it's now in a
structure.

Change-Id: Ic2f1faee4666eea7ae91fd6899cecaa76d0ceb9f
Reviewed-on: https://code.wireshark.org/review/16018
Reviewed-by: Guy Harris <guy@alum.mit.edu>

ui/gtk/main.c

@@ -2068,7 +2068,6 @@ main(int argc, char *argv[])
     gchar               *err_str;
     int                  status;
 #else
-    gboolean             capture_option_specified = FALSE;
 #ifdef _WIN32
 #ifdef HAVE_AIRPCAP
     gchar               *err_str;