[ModernBERT] Never save 'reference_compile' config; should be set based on end user

[tomaarsen]

What does this PR do?

• Never save reference_compile in ModernBertConfig

Details

The ModernBERT architecture uses a reference_compile config option to determine whether various model layers are compiled. However, not every system supports this, so we either 1) use the user's provided value, 2) use the option in the config, or 3) set it automatically based on the user's system.

However, it seems that if you save a model, it will save reference_compile into the config. This is very problematic, as end users who cannot run compilation will be "forced" into compilation (option 2) instead of determining whether compilation is possible (option 3). This is quite annoying for smooth usage.

When this is merged and released, I'll consider writing a script that makes PRs on all ~850 ModernBERT models to remove the reference_compile option from their configs, so it's always just based on the user's system (or manual parameters).

Before submitting

• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
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• Did you write any new necessary tests?

Who can review?

@ArthurZucker

• Tom Aarsen