nix: clean up various things for upcoming GC

Signed-off-by: Raito Bezarius <masterancpp@gmail.com>

modules/nix-daemon.nix

@@ -57,8 +57,8 @@ in
       nrBuildUsers = 128;
 
       settings = {
-        keep-outputs = true;
-        keep-derivations = true;
+        keep-outputs = false;
+        keep-derivations = false;
         use-cgroups = true;
         http-connections = 0;
         auto-allocate-uids = true;
@@ -76,7 +76,7 @@ in
         ];
         experimental-features = [
           "auto-allocate-uids"
-          "ca-derivations"
+          # "ca-derivations" this feature is really extremely broken.
           "cgroups"
           "discard-references"
           "fetch-closure"