There is no need to call UpdateRepoStats in the InsertIssues and
InsertPullRequests function. They are only called during migration by
the CreateIssues and CreateReviews methods of the gitea uploader.

The UpdateRepoStats function will be called by the Finish method of
the gitea uploader after all reviews and issues are inserted. Calling
it before is therefore redundant and the associated SQL requests are
not cheap.

The statistics tests done after inserting an issue or a pull request
are also removed. They predate the implementation of UpdateRepoStats,
back when the calculation of the statistics was an integral part of
the migration function. The UpdateRepoStats is now tested
independantly and these tests are no longer necessary.

Signed-off-by: singuliere <[email protected]>