Housekeeping for GHC 8

- Remove some CPP needed only because of GHC 7.4 (which is not supported
  now, yey)
- Move CPP for GHC 8 to Gap module

test/data/stack-project/new-template.cabal

@@ -16,7 +16,7 @@ cabal-version:       >=1.10
 library
   hs-source-dirs:      src
   exposed-modules:     Lib
-  build-depends:       base >= 4.7 && < 5
+  build-depends:       base
   default-language:    Haskell2010
 
 executable new-template-exe