closes: #10106

## Description
There doesn't seem to be a motivating use case for exposing a maker for a low-level `LocalChainAccount` in the `Orchestrator`, so lets remove it to avoid misdirection. Instead, consumers can call `orch.getChain('agoric').then(c => c.makeAccount())` to get a `LocalOrchestrationAccount`.

### Security Considerations
n/a

### Scaling Considerations
n/a

### Documentation Considerations
docs.agoric.com already reflects this: Agoric/documentation#1208 (comment)

### Testing Considerations
Removing code, so existing tests suffice

### Upgrade Considerations
Library code that will go out in a NPM Orch Release