IsUnitify a signature.

Signed-off-by: Edward Z. Yang <[email protected]>

Author: ezyang

cabal-install/Distribution/Client/InstallPlan.hs

@@ -301,8 +301,7 @@ preexisting pkgid ipkg plan = plan'
 
 -- | Lookup a package in the plan.
 --
-lookup :: (HasUnitId ipkg,   PackageFixedDeps ipkg,
-           HasUnitId srcpkg, PackageFixedDeps srcpkg)
+lookup :: (IsUnit ipkg, IsUnit srcpkg)
        => GenericInstallPlan ipkg srcpkg
        -> UnitId
        -> Maybe (GenericPlanPackage ipkg srcpkg)