Deduplicate hardfork activations info

[fvictorio]

Right now the hardfork activations info lives in two places:

• In the default config of Hardhat (here)
• In edr_eth (here)

We should remove this duplication without affecting the possibility of users configuring these values.

I'm not sure what's the right way to do this. Two ideas:

• Hardhat doesn't pass this anymore unless the user configured something (and this is merged with the defaults in EDR)
• Hardhat still has these defaults but it imports them from EDR (but this means having a "tiny", shared module, because we don't want to load the full EDR during initialization)

The first option is technically a breaking change, but it might be acceptable.