Simplify ghc-pkg's Cabal dependencies

We no longer support building with a compiler that doesn't come with
base 4.

utils/ghc-pkg/ghc-pkg.cabal

@@ -13,32 +13,15 @@ Category: Development
 build-type: Simple
 cabal-version: >=1.2
 
-Flag base4
-    Description: Choose the even newer, even smaller, split-up base package.
-
-Flag base3
-  Description: Choose the new smaller, split-up base package.
-
 Executable ghc-pkg
     Main-Is: Main.hs
     Other-Modules: Version
     Extensions: CPP, ForeignFunctionInterface
 
-    if flag(base4)
-        Build-Depends: base       >= 4   && < 5
-    if flag(base3)
-        Build-Depends: base       >= 3   && < 4
-    if !flag(base3) && !flag(base4)
-        Build-Depends: base       < 3
-
-    if flag(base3) || flag(base4)
-        Build-Depends: directory  >= 1   && < 1.1,
-                       process    >= 1   && < 1.1
-
-    if impl(ghc < 6.9)
-        Build-Depends: extensible-exceptions
-
-    Build-Depends: haskell98,
+    Build-Depends: base       >= 4   && < 5,
+                   directory  >= 1   && < 1.1,
+                   process    >= 1   && < 1.1,
+                   haskell98,
                    filepath,
                    Cabal,
                    binary,