message: Remove unused Signatures table from frontend
diff: #include "node/clientsignatures.h"
  #include "node/consensus.h"
  #include "node/nodes.h"
  -#include "node/signatures.h"
  #include "nodeinterface.h"
  #include "rpcexception.h"
  #include "serialization.h"
  @@ -65,7 +64,6 @@ namespace ccf
  };
  Nodes* nodes;
  - Signatures* signatures;
  ClientSignatures* client_signatures;
  Certs* certs;
  std::optional<Handler> default_handler;
  @@ -187,7 +185,6 @@ namespace ccf
  bool can_forward_) :
  tables(tables_),
  nodes(tables.get<Nodes>(Tables::NODES)),
  - signatures(tables.get<Signatures>(Tables::SIGNATURES)),
  client_signatures(client_sigs_),
  certs(certs_),
  raft(nullptr),
  