libstore: remove unused DerivationGoal::machineName

interpolation of the remote store name into activity text is now done in
the build hook, so we no longer need to send it back to the daemon. this
also reduces the dependency of the daemon on how *exactly* remote builds
are done a little bit, and maybe in time we can make these fully opaque.

Change-Id: Ie51c4f2cd107350fec4ad0a8ef83621ed86db6a2

lix/legacy/build-remote.cc

@@ -449,7 +449,6 @@ kj::Promise<void> Instance::build(BuildContext context)
         assert(builder);
 
         auto ac = context.getResults().initResult().initGood().initAccept();
-        RPC_FILL(ac, setMachineName, builder->storeUri);
         ac.setMachine(kj::heap<AcceptedBuild>(store, drvPath, std::move(*builder), buildLogger));
     } catch (...) {
         RPC_FILL(context.getResults(), initResult, std::current_exception());

lix/libstore/build/derivation-goal.cc

@@ -1086,8 +1086,6 @@ try {
     // the build was accepted by the hook, we can free the slot for another build now
     hookSlot = {};
 
-    machineName = rpc::to<std::string>(buildResp.getAccept().getMachineName());
-
     auto runReq = buildResp.getAccept().getMachine().runRequest();
     /* Tell the hook all the inputs that have to be copied to the
        remote system. */

lix/libstore/build/derivation-goal.hh

@@ -219,11 +219,6 @@ struct DerivationGoal : public Goal
 
     std::map<ActivityId, Activity> builderActivities;
 
-    /**
-     * The remote machine on which we're building.
-     */
-    std::string machineName;
-
     /** Witness type to say that the drvPath has already been added as a temp root */
     struct DrvHasRoot { explicit DrvHasRoot() = default; };
 

lix/libstore/build/hook-instance.capnp

@@ -24,11 +24,10 @@ interface HookInstance {
     union {
       accept :group {
         machine @0 :AcceptedBuild;
-        machineName @1 :Data;
       }
-      postpone @2 :Void;
-      decline @3 :Void;
-      declinePermanently @4 :Void;
+      postpone @1 :Void;
+      decline @2 :Void;
+      declinePermanently @3 :Void;
     }
   }