libadwaita: Fix API docs

Also clean up remnants of gtk-doc from before gi-docgen migration.

pkgs/development/libraries/libadwaita/default.nix

@@ -1,10 +1,7 @@
 { lib
 , stdenv
 , fetchFromGitLab
-, docbook-xsl-nons
 , gi-docgen
-, gtk-doc
-, libxml2
 , meson
 , ninja
 , pkg-config
@@ -37,10 +34,7 @@ stdenv.mkDerivation rec {
   };
 
   nativeBuildInputs = [
-    docbook-xsl-nons
     gi-docgen
-    gtk-doc
-    libxml2 # for xmllint
     meson
     ninja
     pkg-config
@@ -99,8 +93,9 @@ stdenv.mkDerivation rec {
     runHook postCheck
   '';
 
-  postInstall = ''
-    mv $out/share/{doc,gtk-doc}
+  postFixup = ''
+    # Cannot be in postInstall, otherwise _multioutDocs hook in preFixup will move right back.
+    moveToOutput "share/doc" "$devdoc"
   '';
 
   passthru = {