pythongh-870 Added Closing PR section for close reasons (python#877)

* Added Closing PR section

where now we can opt to close as complete or not-planned.

GH issue: python#870
GH blog:
https://github.blog/changelog/2022-05-19-the-new-github-issues-may-19th-update/

* Remove new section and remove github blog hyperlink.

* Modify tracker.rst and restore pullrequest.rst

because the closed reason is for issues and not for pull request.

tracker.rst

@@ -110,7 +110,8 @@ after a consensus has been reached amongst the core developers is unlikely to
 win any converts.
 
 As a reminder, issues closed by a core developer have already been carefully
-considered. Please do not reopen a closed issue.
+considered. Please do not reopen a closed issue. An issue can be closed with
+reason either as ``complete`` or ``not planned``.
 
 .. _helptriage: