Do not depend on hspec-discover (the haskell library), as that is empty
anyways. We ensure that the hspec-discover binary is available via
control/debian.

Index: b/hspec.cabal
===================================================================
--- a/hspec.cabal
+++ b/hspec.cabal
@@ -47,7 +47,6 @@ library
       QuickCheck >=2.12
     , base ==4.*
     , hspec-core ==2.11.9
-    , hspec-discover ==2.11.9
     , hspec-expectations ==0.8.4.*
   exposed-modules:
       Test.Hspec
