EVM Node: Make the observer mode use the read-only context for RPCs

This changeset has several short term benefits

1. Relying on the read-write Evm_context module to implement the RPC services means that everytime we need to checkout an EVM state, we need to go through the worker.
2. This is simpler, and remove code.
3. We want to move towards spawning RPC nodes anyway, and this is a move in that direction.

Semantically, this is a no-op patch, but pragramtically, it is possible that RPCs targeting the latest state becomes a bit slower.

Manually testing the MR

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).
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