fix enclave-account/root ambiguity

[brenzi]

We still use legacy derivation of a superuser granted to the enclave signer.

What currently is bad:

• state is initialized with enclave account =primary worker's enclave signer
  • this makes no sense. every enclave with valid MRENCLAVE has superuser rights on the state. the primary worker has no special role here
  • this could lead to failures: if a secondary validateer tries to call set_timestamp, for example
• we instantiate the sudo pallet in the sgx_runtime, but we don't need it, actually. some tests do, but could be done otherwise

the only thing we actually need is a way to authorize the current enclave: ensure_enclave_signer_account

Solution:

• sync the current set of validateers for this shard into the state with get_storage_hashes_to_update on integritee parentchain
• modify ensure_enclave_signer_account to verify set membership instead