• DISABLE_VALIDATOR_REGISTRATIONS no longer affects how the remote signer
  loads its public keys. In v3.1.11 the flag made RemoteSignerKeystore fall
  back to querying the signer API, which failed on startup for deployments
  using REMOTE_SIGNER_USE_DEPOSIT_DATA=true.
• An empty deposit_data.json ([]) is now accepted when registrations are
  disabled. The deposit data merkle tree is no longer built, so the file is
  only read for its public keys. Note that exit signature rotation stops while
  the file is empty.
• The deposit data file is required only when some code path actually reads it.
  A leftover REMOTE_SIGNER_USE_DEPOSIT_DATA=true no longer blocks startup in
  API registration mode or with local keystores.
• stakeable_assets and unused_validator_keys keep being exported when
  registrations are disabled.