[torchlib] Do not register rsub (#1907)

Remove rsub since it is handled by decomp, and torch doesn't have a type
promotion rule for rsub so we use sub instead.

Tested with 

```python
import torch


class Model(torch.nn.Module):
    def forward(self, x):
        return 1 - x


ep = torch.export.export(Model(), (torch.tensor(1),))
print(ep)

program = torch.onnx.export(Model(), (torch.tensor(1),), dynamo=True)
print(program)

```

Author: justinchuby

onnxscript/function_libs/torch_lib/ops/core.py

@@ -7352,18 +7352,11 @@ def aten_rsqrt(self: TFloat) -> TFloat:
     return op.Reciprocal(op.Sqrt(self))
 
 
-@torch_op(("aten::rsub.Tensor", "aten::rsub.Scalar"))
+# Do not register rsub. It will be decomposed and type promoted by torch
 def aten_rsub(self: TReal, other: TReal, alpha: float = 1.0) -> TReal:
     """rsub.Tensor(Tensor self, Tensor other, *, Scalar alpha=1) -> Tensor"""
 
-    return op.Sub(other, op.Mul(self, alpha))
-
-
-@torch_op(("aten::rsub.Tensor", "aten::rsub.Scalar"), trace_only=True, complex=True)
-def aten_rsub_complex(self: TReal, other: TReal, alpha: float = 1.0) -> TReal:
-    """rsub.Tensor(Tensor self, Tensor other, *, Scalar alpha=1) -> Tensor"""
-
-    return aten_rsub(self, other, alpha)
+    raise NotImplementedError
 
 
 @torch_op("aten::scalar_tensor", trace_only=True)

tests/function_libs/torch_lib/ops_test_data.py

@@ -1360,8 +1360,6 @@ def _where_input_wrangler(
     ),
     TorchLibOpInfo("round_decimals", core_ops.aten_round_decimals),
     TorchLibOpInfo("rsqrt", core_ops.aten_rsqrt),
-    TorchLibOpInfo("rsub", core_ops.aten_rsub),
-    TorchLibOpInfo("rsub", core_ops.aten_rsub_complex, complex=True),
     TorchLibOpInfo(
         "scalar_tensor",
         core_ops.aten_scalar_tensor,