Fix extra "." in CmdSearch::getDefaultFlakeAttrPaths

No other getDefaultFlakeAttrPaths implementation has this trailing dot,
and the dot can show up in error messages like:

  error: flake '...' does not provide attribute 'packages.x86_64-linux.', ...

src/nix/search.cc

@@ -56,8 +56,8 @@ struct CmdSearch : InstallableCommand, MixJSON
     Strings getDefaultFlakeAttrPaths() override
     {
         return {
-            "packages." + settings.thisSystem.get() + ".",
-            "legacyPackages." + settings.thisSystem.get() + "."
+            "packages." + settings.thisSystem.get(),
+            "legacyPackages." + settings.thisSystem.get()
         };
     }