Remove editors_per_user function from database and include it within API script

[kshitijrajsharma]

@kshitijrajsharma the editors_per_user function is the remaining dblink function from the earlier TM stats implementation by @omranlm. But since we can now set up and talk to the TM database directly via the API, I agree it is better to remove all dblink functions.

Originally posted by @d-rita in #329 (comment)