SR: remove PVM initial state hash

Context

Copy-pasting the commit description:

It was necessary when we verified the proof at origination time, to
make sure the proof started from the expected initial state. As we
produce the proof in the protocol, by choosing the initial state, we
don't need to ensure this equality at runtime.

Manually testing the MR

I'll rely on the CI to test this

Checklist

• Document the interface of any function added or modified (see the coding guidelines)
• Document any change to the user interface, including configuration parameters (see node configuration)
• Provide automatic testing (see the testing guide).
• For new features and bug fixes, add an item in the appropriate changelog (docs/protocols/alpha.rst for the protocol and the environment, CHANGES.rst at the root of the repository for everything else).
• Select suitable reviewers using the Reviewers field below.
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