Clarify when the DVC's anti-slashing DB intialisation should take place.

The [Anti-Slashing Measures at the DVC](https://github.com/ethereum/distributed-validator-specs/blob/dev/src/dvspec/README.md#anti-slashing-measures-at-the-dvc) section of the [Ethereum Distributed Validator Specification](https://github.com/ethereum/distributed-validator-specs/blob/dev/src/dvspec/README.md) requires that DVCs initialises its anti-slashing DB to the VC's anti-slashing DB.

Currently, the specification is open for interpretation on the following points:
1. Should the DVC's anti-slashing DB initialisation occur every time that the DVC is started?
2. Should the DVC's anti-slashing DB initialisation occur only the first time that the DVC is started?
3. Should the VC's anti-slashing protection be disabled and rely entirely on the DVC's anti-slashing protection?
- If so and if behaviour 1 above is the desired one, then the VC still needs to keep updating its anti-slashing DB albeit no check is preferred when signing.