Enhance memory management in dup node deletion

In q_delete_dup, replace the conditional check and freeing of 'prob'
with a more clear approach. The updated code uses `free(prob)` directly,
followed by updating 'prob' with the strdup result from 'cur->val'

queue.c

@@ -159,10 +159,7 @@ bool q_delete_dup(struct list_head *head)
                 continue;
             } else {
                 // Update the prob if cur and next have the same string
-                if (prob) {
-                    free(prob);
-                    prob = NULL;
-                }
+                free(prob);
                 prob = strdup(cur->value);
             }
         }