Remove `from_state` method from `BackendSimulator`

[esantorella]

Summary: Context:

BackendSimulator.from_state is a way of initializing a BackendSimulator that is less useful now that BackendSimulator has an options attribute (D66102162), and it is not used outside unit tests.

This PR:

• Removes BackendSimulator.from_state

Differential Revision: D66103291

[facebook-github-bot]

This pull request was exported from Phabricator. Differential Revision: D66103291

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 95.69%. Comparing base (0cab5d2) to head (18dfec6).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #3079 +/- ## ========================================== - Coverage 95.70% 95.69% -0.01% ========================================== Files 487 488 +1 Lines 49525 49510 -15 ========================================== - Hits 47396 47381 -15 Misses 2129 2129 ```

:umbrella: View full report in Codecov by Sentry.
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[facebook-github-bot]

This pull request has been merged in facebook/Ax@7b671dc9e042a7580905d58f0994a0cd25d45673.