[5620660][ONNX] Remove toposort after quantization

[gcunhase]

What does this PR do?

Type of change: Bug fix

Overview: Loading the model with ONNX graphsurgeon after quantization and FP16 conversion results in an ONNX model with FP16 output instead of FP32 even though the Cast_to_fp32 layer was correctly placed in the graph output. This PR fixes that issue.

Usage

$ python -m modelopt.onnx.quantization --onnx_path=$MODEL_NAME.onnx --high_precision_dtype=fp16

Testing

See bug 5620660.

Before your PR is "Ready for review"

• Make sure you read and follow Contributor guidelines and your commits are signed.
• Is this change backward compatible?: Yes
• Did you write any new necessary tests?: No
• Did you add or update any necessary documentation?: No
• Did you update Changelog?: No

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 73.52%. Comparing base (5adb9ba) to head (bf42d85).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #524      +/-   ##
==========================================
- Coverage   73.52%   73.52%   -0.01%     
==========================================
  Files         181      181              
  Lines       18207    18204       -3     
==========================================
- Hits        13387    13384       -3     
  Misses       4820     4820              

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