Revert "Add a separate manual job"

This reverts commit 5e3ad1d. Manual
generation now depends on the 'nix' command.

flake.nix

@@ -144,6 +144,11 @@
 
           installFlags = "sysconfdir=$(out)/etc";
 
+          postInstall = ''
+            mkdir -p $doc/nix-support
+            echo "doc manual $doc/share/doc/nix/manual" >> $doc/nix-support/hydra-build-products
+          '';
+
           doInstallCheck = true;
           installCheckFlags = "sysconfdir=$(out)/etc";
 
@@ -210,25 +215,6 @@
         # Perl bindings for various platforms.
         perlBindings = nixpkgs.lib.genAttrs systems (system: nixpkgsFor.${system}.nix.perl-bindings);
 
-        # Separate build for just the manual.
-        manual =
-          with nixpkgsFor.x86_64-linux;
-          stdenv.mkDerivation {
-            name = "nix-manual-${version}";
-            src = self;
-            buildInputs = [ mdbook ];
-            configurePhase = ":";
-            buildPhase = ":";
-            installPhase =
-              ''
-                touch Makefile.config
-                docdir=$out/share/doc/nix
-                make docdir=$docdir doc_generate=yes $docdir/manual/index.html
-                mkdir -p $out/nix-support
-                echo "doc manual $docdir/manual" >> $out/nix-support/hydra-build-products
-              '';
-          };
-
         # Binary tarball for various platforms, containing a Nix store
         # with the closure of 'nix' package, and the second half of
         # the installation script.