Don't anticipate hash algo without hash in derivation for now

When we merge with master, the new lack of string types make this case
impossible (after parsing). Later, when we actually implemenent
CA-derivations, we'll change the types to allow that.

src/libstore/derivations.cc

@@ -359,21 +359,9 @@ DerivationType BasicDerivation::type() const
         outputs.begin()->second.hash != "")
     {
         return DerivationType::CAFixed;
+    } else {
+        return DerivationType::Regular;
     }
-
-    auto const algo = outputs.begin()->second.hashAlgo;
-    if (algo != "") {
-        throw Error("Invalid mix of CA and regular outputs");
-    }
-    for (auto & i : outputs) {
-        if (i.second.hash != "") {
-            throw Error("Non-fixed-output derivation has fixed output");
-        }
-        if (i.second.hashAlgo != "") {
-            throw Error("Invalid mix of CA and regular outputs");
-        }
-    }
-    return DerivationType::Regular;
 }