Clean up 'Flow talk page manager' related code

Authored by Legoktm.


Clean up 'Flow talk page manager' related code

  • Always use the hardcoded English version so the username is the same

across all wikis.

  • Use accounts even if we didn't create them. If a malicious user takes

the name, they will be locked out due to the UserGetReservedNames

    • Previous detection only checked if the user was a bot, which can easily be spoofed.
  • If CentralAuth is installed, attach new users to the global account.
  • Remove special casing for PHPUnit tests :)

Bug: T101300
Bug: T107329
Change-Id: I3f01fa40fcb364382caddad268d1d90a4d37ad9a
(cherry picked from commit 5c84c341117e956bdc1e9306058e03c43315f7bc)