Remove a test for the specific kind of exception for nhc98 compatibility

This was the check for ghc-pkg failing. We cannot check for the
exception being an ExitException since that assumes ghc's
representation of the Exception type, whereas nhc98 defines:
type Exception = IOError

Distribution/Simple/GHC.hs

@@ -99,9 +99,7 @@ import System.FilePath          ( (</>), (<.>), takeExtension,
                                   takeDirectory, replaceExtension, splitExtension )
 import System.IO (openFile, IOMode(WriteMode), hClose, hPutStrLn)
 import Control.Exception as Exception
-         ( Exception(ExitException), catch, handle, try, throwIO )
-import System.Exit
-         ( ExitCode(..) )
+         ( catch, handle, try )
 
 -- -----------------------------------------------------------------------------
 -- Configuring
@@ -283,13 +281,11 @@ getInstalledPackages' verbosity packagedbs conf
   sequence
     [ do str <- rawSystemProgramStdoutConf verbosity ghcPkgProgram conf
                   ["describe", "*", packageDbGhcPkgFlag packagedb]
-           `Exception.catch` \exception -> case exception of
-             ExitException (ExitFailure 1) -> die $
+           `Exception.catch` \_ -> die $
                   "ghc-pkg describe * failed. If you are using ghc-6.9 "
                ++ "and have an empty user package database then this "
                ++ "is probably due to ghc bug #2201. The workaround is to "
                ++ "register at least one package in the user package db."
-             _ -> throwIO exception
          case parsePackages str of
 	   Left ok -> return (packagedb, ok)
 	   _       -> die "failed to parse output of 'ghc-pkg describe *'"