fix: bad error message for nix store delete --ignore-liveness

Found at work; the message implies you aren't trusted-user when it
actually is that ignore-liveness is always rejected by the daemon.

Whether this command is actually a good idea varies substantially of
course.

Change-Id: I47a710b835fd082ac85a24c7329f21117b1341ee

lix/libstore/daemon.cc

@@ -733,7 +733,7 @@ static void performOp(AsyncIoRoot & aio, TunnelLogger * logger, ref<Store> store
 
         logger->startWork();
         if (options.ignoreLiveness)
-            throw Error("you are not allowed to ignore liveness");
+            throw Error("ignore-liveness is not supported via the Lix daemon; try running the command again with `--store local` and as the user that owns the Nix store (usually root)");
         auto & gcStore = require<GcStore>(*store);
         aio.blockOn(gcStore.collectGarbage(options, results));
         logger->stopWork();