Parse CA derivations using new output variants

We no longer need `ParsedDerivation` because everything libstore needs
to know about is in the `BasicDerivation` proper.

src/libstore/build.cc

@@ -1195,7 +1195,7 @@ void DerivationGoal::haveDerivation()
 
     parsedDrv = std::make_unique<ParsedDerivation>(drvPath, *drv);
 
-    if (parsedDrv->contentAddressed()) {
+    if (drv->type() == DerivationType::CAFloating) {
         settings.requireExperimentalFeature("ca-derivations");
         throw UnimplementedError("ca-derivations isn't implemented yet");
     }

src/libstore/parsed-derivations.cc

@@ -117,9 +117,4 @@ bool ParsedDerivation::substitutesAllowed() const
     return getBoolAttr("allowSubstitutes", true);
 }
 
-bool ParsedDerivation::contentAddressed() const
-{
-    return getBoolAttr("__contentAddressed", false);
-}
-
 }

src/libstore/parsed-derivations.hh

@@ -34,8 +34,6 @@ public:
     bool willBuildLocally() const;
 
     bool substitutesAllowed() const;
-
-    bool contentAddressed() const;
 };
 
 }