Remove the duplicate check_model message when displaying

ghstack-source-id: 35dc813
Pull Request resolved: #882

)

Stack from [ghstack](https://github.com/ezyang/ghstack) (oldest at
bottom):
* #883
* #882
* __->__ #881

The torchscript ONNX graph generator creates numeric value names by
default (`0`, `1`). These are not legal ONNX tensor names, since ONNX
requires the names to be valid C variable names. This change updates the
names by prepending a prefix `_val_` or `_const_` to make them valid
ONNX names. It also improves readability by making the names less likely
to be confused with shape values.

I decided to use the `_` prefix to reduce the chance of name collision
with FX names.

After:

```
<
   ir_version: 8,
   opset_import: ["" : 18],
   producer_name: "pytorch",
   producer_version: "2.1.0"
>
torch_jit (float[5,5,5,5] input_0, int64[2] input_1_3) => (float[5,5,5,2] _val_10) {
   _val_2 = Transpose <perm = [0, 1, 2, 3]> (input_0)
   _val_3 = Max (input_1_3)
   _val_4 = Shape <start = 0> (_val_3)
   _val_5 = Expand (input_1_3, _val_4)
   _const_6 = Constant <value = int64 {-1}> ()
   _val_7 = Unsqueeze (_val_5, _const_6)
   _val_8 = Concat <axis = -1> (_val_7)
   _val_9 = GatherND <batch_dims = 0> (_val_2, _val_8)
   _val_10 = Transpose <perm = [0, 1, 2, 3]> (_val_9)
}
```

Before:

```
<
   ir_version: 8,
   opset_import: ["" : 18],
   producer_name: "pytorch",
   producer_version: "2.1.0"
>
torch_jit (float[5,5,5,5] input_0, int64[2] input_1_3) => (float[5,5,5,2] 10) {
   2 = Transpose <perm = [0, 1, 2, 3]> (input_0)
   3 = Max (input_1_3)
   4 = Shape <start = 0> (3)
   5 = Expand (input_1_3, 4)
   6 = Constant <value = int64 {-1}> ()
   7 = Unsqueeze (5, 6)
   8 = Concat <axis = -1> (7)
   9 = GatherND <batch_dims = 0> (2, 8)
   10 = Transpose <perm = [0, 1, 2, 3]> (9)
}
```