When deleting a closed issue, we should update both `NumIssues`and
`NumClosedIssues`, or `NumOpenIssues`(`= NumIssues -NumClosedIssues`)
will be wrong. It's the same for pull requests.
Releated to #21557.
Alse fixed two harmless problems:
- The SQL to check issue/PR total numbers is wrong, that means it will
update the numbers even if they are correct.
- Replace legacy `num_issues = num_issues + 1` operations with
`UpdateRepoIssueNumbers`.
74874d065f