Remove Nix integration

It's the follow-up to #9205
and completely removes the Nix integration feature

Author: zlonast

cabal-install/cabal-install.cabal

@@ -174,7 +174,6 @@ library
         Distribution.Client.Main
         Distribution.Client.Manpage
         Distribution.Client.ManpageFlags
-        Distribution.Client.Nix
         Distribution.Client.NixStyleOptions
         Distribution.Client.PackageHash
         Distribution.Client.ParseUtils

cabal-install/src/Distribution/Client/Config.hs

@@ -368,7 +368,6 @@ instance Semigroup SavedConfig where
           , globalLogsDir = combine globalLogsDir
           , globalIgnoreExpiry = combine globalIgnoreExpiry
           , globalHttpTransport = combine globalHttpTransport
-          , globalNix = combine globalNix
           , globalStoreDir = combine globalStoreDir
           , globalProgPathExtra = lastNonEmptyNL globalProgPathExtra
           }
@@ -1112,7 +1111,6 @@ commentSavedConfig = do
           { savedGlobalFlags =
               defaultGlobalFlags
                 { globalRemoteRepos = toNubList [defaultRemoteRepo]
-                , globalNix = mempty
                 }
           , savedInitFlags =
               mempty

cabal-install/src/Distribution/Client/GlobalFlags.hs

@@ -93,8 +93,6 @@ data GlobalFlags = GlobalFlags
   , globalIgnoreExpiry :: Flag Bool
   -- ^ Ignore security expiry dates
   , globalHttpTransport :: Flag String
-  , globalNix :: Flag Bool
-  -- ^ Integrate with Nix
   , globalStoreDir :: Flag FilePath
   , globalProgPathExtra :: NubList FilePath
   -- ^ Extra program path used for packagedb lookups in a global context (i.e. for http transports)
@@ -115,7 +113,6 @@ defaultGlobalFlags =
     , globalLogsDir = mempty
     , globalIgnoreExpiry = Flag False
     , globalHttpTransport = mempty
-    , globalNix = Flag False
     , globalStoreDir = mempty
     , globalProgPathExtra = mempty
     }