Get rid of filterDrvOutputs

We don't need it any more, because we only used it in the
single-wanted-output `DerivationGoal`.

src/libstore/build/derivation-goal.cc

@@ -359,9 +359,8 @@ Goal::Done DerivationGoal::done(BuildResult::Status status, SingleDrvOutputs bui
     mcExpectedBuilds.reset();
 
     if (buildResult.success()) {
-        auto wantedBuiltOutputs = filterDrvOutputs(OutputsSpec::Names{wantedOutput}, std::move(builtOutputs));
+        assert(!builtOutputs.empty());
-        assert(!wantedBuiltOutputs.empty());
+        buildResult.builtOutputs = std::move(builtOutputs);
-        buildResult.builtOutputs = std::move(wantedBuiltOutputs);
         if (status == BuildResult::Built)
             worker.doneBuilds++;
     } else {

src/libstore/include/nix/store/realisation.hh

@@ -102,13 +102,6 @@ typedef std::map<OutputName, Realisation> SingleDrvOutputs;
  */
 typedef std::map<DrvOutput, Realisation> DrvOutputs;
 
-/**
- * Filter a SingleDrvOutputs to include only specific output names
- *
- * Moves the `outputs` input.
- */
-SingleDrvOutputs filterDrvOutputs(const OutputsSpec &, SingleDrvOutputs &&);
-
 struct OpaquePath
 {
     StorePath path;

src/libstore/realisation.cc

@@ -135,18 +135,6 @@ size_t Realisation::checkSignatures(const PublicKeys & publicKeys) const
     return good;
 }
 
-SingleDrvOutputs filterDrvOutputs(const OutputsSpec & wanted, SingleDrvOutputs && outputs)
-{
-    SingleDrvOutputs ret = std::move(outputs);
-    for (auto it = ret.begin(); it != ret.end();) {
-        if (!wanted.contains(it->first))
-            it = ret.erase(it);
-        else
-            ++it;
-    }
-    return ret;
-}
-
 StorePath RealisedPath::path() const
 {
     return std::visit([](auto && arg) { return arg.getPath(); }, raw);