Block stackage-curator/stackage2nix.

Unfortunately, there is a build failure in stackage-curator
and the lesser version has some compat problem which is related
to the GHC version (I think!). So, I'm blocking for now.

stackage2nix suffers the same fate since it relies on stackage-curator.

Ping @4e6, @snoyman.

build-constraints.yaml

@@ -281,7 +281,7 @@ packages:
         - persistent-postgresql
         - persistent-sqlite
         - persistent-template
-        - stackage-curator
+        # - stackage-curator
         - store
         - stm-conduit
         - wai-websockets
@@ -3314,7 +3314,8 @@ packages:
         - ghost-buster
 
     "typeable.io <makeit@typeable.io>":
-        - stackage2nix
+        []
+        # - stackage2nix
 
     "Jeremy Huffman <jeremy@jeremyhuffman.com> @jeremyjh":
         - higher-leveldb
@@ -3382,10 +3383,6 @@ packages:
         - llvm-hs < 5.0.0
         - llvm-hs-pure == 4.1.0.0
 
-        # https://github.com/fpco/stackage-curator/issues/46
-        - stackage-curator < 0.15.0.0
-        - stackage2nix < 0.3.0
-
 # end of packages
 
 # Package flags are applied to individual packages, and override the values of