Migrate ghcup-gen to haskell/ghcup-metadata

ghcup.cabal

@@ -43,6 +43,11 @@ flag internal-downloader
   default:     False
   manual:      True
 
+flag no-exe
+  description: Don't build any executables 
+  default:     False
+  manual:      True
+
 library
   exposed-modules:
     GHCup
@@ -252,51 +257,8 @@ executable ghcup
 
   if os(windows)
     cpp-options: -DIS_WINDOWS
-
-executable ghcup-gen
-  main-is:            Main.hs
-  hs-source-dirs:     app/ghcup-gen
-  other-modules:      Validate
-  default-language:   Haskell2010
-  default-extensions:
-    DeriveGeneric
-    LambdaCase
-    MultiWayIf
-    NamedFieldPuns
-    PackageImports
-    QuasiQuotes
-    RecordWildCards
-    ScopedTypeVariables
-    StrictData
-    TupleSections
-    TypeApplications
-    TypeFamilies
-    ViewPatterns
-
-  ghc-options:
-    -Wall -fwarn-tabs -fwarn-incomplete-uni-patterns
-    -fwarn-incomplete-record-updates -threaded
-
-  build-depends:
-    , base                  >=4.13     && <5
-    , bytestring            ^>=0.10
-    , containers            ^>=0.6
-    , filepath              ^>=1.4.2.1
-    , ghcup
-    , haskus-utils-variant  >=3.0      && <3.2
-    , libarchive            ^>=3.0.3.0
-    , mtl                   ^>=2.2
-    , optics                ^>=0.4
-    , optparse-applicative  >=0.15.1.0 && <0.17
-    , pretty                ^>=1.1.3.1
-    , pretty-terminal       ^>=0.1.0.0
-    , regex-posix           ^>=0.96
-    , resourcet             ^>=1.2.2
-    , safe-exceptions       ^>=0.1
-    , text                  ^>=1.2.4.0
-    , transformers          ^>=0.5
-    , versions              >=4.0.1    && <5.1
-    , yaml-streamly         ^>=0.12.0
+  if flag(no-exe)
+    buildable: False
 
 test-suite ghcup-test
   type:               exitcode-stdio-1.0