[Bug]: PostGradPassManager should not reference the compilation_config

[zou3519]

Your current environment

main

🐛 Describe the bug

Inductor configs need to be serializable and deepcopy-able, the PostGradPassManager is added to the Inductor config, and the CompilationConfig holds some nn.Modules. The Inductor config gets deepcopied sometimes, plus we have observed OOMs due to nn.Modules being in the PostGradPassManager.

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[ProExpertProg]

Resolved by #27041