haskell: fix package sets based on integer-simple

Fixes mass build failures in these package sets,
due to "unknown pacakge: integer-simple".

Attributes that demonstrate this (see before/after):

* haskell.packages.integer-simple.ghc843.hello
* haskell.packages.integer-simple.ghc802.scientific

The second one is from the NixOS manual, FWIW.