kdePackages.akonadi-search: directly pass cargoRoot to fetcher

pkgs/kde/gear/akonadi-search/default.nix

···
   cargoRoot = "agent/rs/htmlparser";
 
   cargoDeps = rustPlatform.fetchCargoVendor {
-    inherit pname version;
+    inherit pname version cargoRoot;
     src = sources.${pname};
-    sourceRoot = "${pname}-${version}/${cargoRoot}";
     hash = "sha256-hdm4LfQcs4TTfBLzlZYJ0uzqfLxMXuYQExLGJg81W2U=";
   };