chore: remove unused sol WS settings

[kylezs]

Pull Request

Checklist

Please conduct a thorough self-review before opening the PR.

• [x] I am confident that the code works.
• [x] I have written sufficient tests.
• [x] I have written and tested required migrations.
• [x] I have updated documentation where appropriate.

Summary

Remove unused sol WS settings

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 30.00000% with 14 lines in your changes missing coverage. Please review.

Project coverage is 70%. Comparing base (713c36f) to head (946f115). Report is 1 commits behind head on release/1.6.

Files with missing lines	Patch %	Lines
engine/src/settings.rs	50%	3 Missing and 3 partials :warning:
engine/src/sol/retry_rpc.rs	0%	4 Missing :warning:
engine/src/witness/sol/sol_deposits.rs	0%	2 Missing :warning:
engine/src/witness/sol.rs	0%	1 Missing :warning:
engine/src/witness/sol/nonce_witnessing.rs	0%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## release/1.6 #5239 +/- ## =========================================== Coverage 70% 70% =========================================== Files 481 481 Lines 86274 86261 -13 Branches 86274 86261 -13 =========================================== - Hits 60429 60422 -7 + Misses 22554 22545 -9 - Partials 3291 3294 +3 ```

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