Remove quantization_config in config.json from original deepseek models

[Edwardf0t1]

What does this PR do?

Type of change: Bug fix

Overview: DeepSeek original checkpoints may include a quantization_config field in config.json
(describing the source checkpoint's quantization). When we export ModelOpt quantization
configs to hf_quant_config.json, leaving the original quantization_config in place can
be confusing. Add a function to remove it.

Usage

# Add a code snippet demonstrating how to use this

Testing

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• 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?: Yes/No
• Did you add or update any necessary documentation?: Yes/No
• Did you update Changelog?: Yes/No

Additional Information

Resolve nvbug https://nvbugspro.nvidia.com/bug/5736665

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 74.66%. Comparing base (307fe71) to head (52a2230).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #753   +/-   ##
=======================================
  Coverage   74.66%   74.66%           
=======================================
  Files         192      192           
  Lines       18975    18975           
=======================================
  Hits        14167    14167           
  Misses       4808     4808           

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