Specialize and delete code not needed by SolverInstallPlan.

Now we monomorphize SolverInstallPlan so that its data structures
are non-parametric, and delete functions that are not needed.
Specifically:

    - GenericPlanPackage -> SolverPlanPackage, lose the
      type parameters, lose the Processing/Installed/Failed
      constructors (this makes some partial functions total! Yay!)

    - GenericInstallPlan -> SolverInstallPlan

    - PlanProblem -> SolverPlanProblem

    - Deleted ready, processing, completed, failed,
      preexisting
Signed-off-by: Edward Z. Yang <ezyang@cs.stanford.edu>

cabal-install/Distribution/Client/Install.hs

@@ -457,7 +457,7 @@ pruneInstallPlan pkgSpecifiers =
   either (Fail . explain) Done
   . SolverInstallPlan.remove (\pkg -> packageName pkg `elem` targetnames)
   where
-    explain :: [SolverInstallPlan.PlanProblem ipkg srcpkg iresult ifailure] -> String
+    explain :: [SolverInstallPlan.SolverPlanProblem] -> String
     explain problems =
       "Cannot select only the dependencies (as requested by the "
       ++ "'--only-dependencies' flag), "

cabal-install/Distribution/Client/InstallPlan.hs

@@ -796,8 +796,6 @@ configureInstallPlan solverPlan =
 
         SolverInstallPlan.Configured  pkg ->
           Configured (configureSolverPackage mapDep pkg)
-
-        _ -> error "configureInstallPlan: unexpected package state"
   where
     configureSolverPackage :: (UnitId -> UnitId)
                            -> SolverPackage UnresolvedPkgLoc

cabal-install/Distribution/Client/ProjectPlanning.hs

@@ -1025,8 +1025,6 @@ elaborateInstallPlan platform compiler compilerprogdb
             InstallPlan.Configured
               (elaborateSolverPackage mapDep pkg)
 
-          _ -> error "elaborateInstallPlan: unexpected package state"
-
     elaborateSolverPackage :: (UnitId -> UnitId)
                            -> SolverPackage UnresolvedPkgLoc
                            -> ElaboratedConfiguredPackage

cabal-install/tests/UnitTests/Distribution/Solver/Modular/DSL.hs

@@ -48,7 +48,6 @@ import Language.Haskell.Extension (Extension(..), Language)
 import Distribution.Client.Dependency
 import Distribution.Client.Dependency.Types
 import Distribution.Client.Types
-import qualified Distribution.Client.InstallPlan       as CI.InstallPlan
 import qualified Distribution.Client.SolverInstallPlan as CI.SolverInstallPlan
 
 import           Distribution.Solver.Types.ComponentDeps (ComponentDeps)
@@ -473,10 +472,10 @@ exResolve db exts langs pkgConfigDb targets solver mbj indepGoals reorder
 
 extractInstallPlan :: CI.SolverInstallPlan.SolverInstallPlan
                    -> [(ExamplePkgName, ExamplePkgVersion)]
-extractInstallPlan = catMaybes . map confPkg . CI.InstallPlan.toList
+extractInstallPlan = catMaybes . map confPkg . CI.SolverInstallPlan.toList
   where
     confPkg :: CI.SolverInstallPlan.SolverPlanPackage -> Maybe (String, Int)
-    confPkg (CI.InstallPlan.Configured pkg) = Just $ srcPkg pkg
+    confPkg (CI.SolverInstallPlan.Configured pkg) = Just $ srcPkg pkg
     confPkg _                               = Nothing
 
     srcPkg :: SolverPackage UnresolvedPkgLoc -> (String, Int)