Docs: remove descriptor page from nitignore

Author: Boyeep

Doc/tools/.nitignore

@@ -2,7 +2,6 @@
 # as tested on the CI via check-warnings.py in reusable-docs.yml.
 # Keep lines sorted lexicographically to help avoid merge conflicts.
 
-Doc/c-api/descriptor.rst
 Doc/c-api/init_config.rst
 Doc/c-api/intro.rst
 Doc/c-api/stable.rst