Revert "[Dynamo] Trace enter/exit of TorchFunctionModes (#135422)" (#136590)

This reverts commit 7743149b2be4a9eba7e0997ccdc6abe552bec266.

Reverts
* https://github.com/pytorch/pytorch/pull/135503
* https://github.com/pytorch/pytorch/pull/135502
* https://github.com/pytorch/pytorch/pull/135422

This passes this test. Earlier, the getitem would stay like a getitem in the Fx graph. But now the fake tensor propagations fails saying that .item is called. It seems that torch function is not getting triggered while fake tensor propagation.

```
import torch
from torch.nn.attention.flex_attention import BlockMask, _mask_mod_signature, _score_mod_signature, flex_attention
from torch._inductor.lowering import make_pointwise, register_lowering
from torch._inductor.virtualized import ops
from torch.nn.attention.flex_attention import create_block_mask

torch.set_default_device('cuda')

flex_attention = torch.compile(flex_attention, dynamic=False)

prefix_lengths = torch.arange(8)
def prefix_lm(b, h, q, kv):
    return prefix_lengths[b] >= kv

mask = create_block_mask(prefix_lm, 8, None, 512, 512, _compile=True)
```

Pull Request resolved: https://github.com/pytorch/pytorch/pull/136590
Approved by: https://github.com/Chillee

torch/_dynamo/testing.py

@@ -187,7 +187,6 @@ def debug_insert_nops(
         local_scope=locals(),
         global_scope=globals(),
         f_code=frame.f_code,
-        torch_function_mode_stack=[],
     )
 
     return GuardedCode(code, CheckFunctionManager(graph).check_fn, CompileId(0, 0))