emacs.pkgs.ghc-mod: move to a dedicated directory

There is no tangible reason to pollute a file like manual-packages with full
descriptions of expressions. `callPackage` exists for a reason :)

pkgs/applications/editors/emacs/elisp-packages/ghc-mod/default.nix

@@ -0,0 +1,27 @@
+{ lib
+, pkgs
+, melpaBuild
+, haskellPackages
+, writeText
+}:
+
+melpaBuild {
+  pname = "ghc";
+
+  inherit (haskellPackages.ghc-mod) version src;
+
+  packageRequires = [ haskell-mode ];
+
+  propagatedUserEnvPkgs = [ haskellPackages.ghc-mod ];
+
+  recipe = writeText "recipe" ''
+    (ghc-mod :repo "DanielG/ghc-mod" :fetcher github :files ("elisp/*.el"))
+  '';
+
+  fileSpecs = [ "elisp/*.el" ];
+
+  meta = {
+    description = "An extension of haskell-mode that provides completion of symbols and documentation browsing";
+    license = lib.licenses.bsd3;
+  };
+}

pkgs/applications/editors/emacs/elisp-packages/manual-packages.nix

@@ -4,27 +4,7 @@ self: with self; {
 
   elisp-ffi = callPackage ./elisp-ffi { };
 
-  ghc-mod = melpaBuild {
-    pname = "ghc";
-    version = pkgs.haskellPackages.ghc-mod.version;
-
-    src = pkgs.haskellPackages.ghc-mod.src;
-
-    packageRequires = [ haskell-mode ];
-
-    propagatedUserEnvPkgs = [ pkgs.haskellPackages.ghc-mod ];
-
-    recipe = pkgs.writeText "recipe" ''
-      (ghc-mod :repo "DanielG/ghc-mod" :fetcher github :files ("elisp/*.el"))
-    '';
-
-    fileSpecs = [ "elisp/*.el" ];
-
-    meta = {
-      description = "An extension of haskell-mode that provides completion of symbols and documentation browsing";
-      license = lib.licenses.bsd3;
-    };
-  };
+  ghc-mod = callPackage ./elisp-ffi { };
 
   haskell-unicode-input-method = let
     rev = "d8d168148c187ed19350bb7a1a190217c2915a63";