Cleanup debugging code for isTalkpageManagerUser
- Remove ArticleEditUpdateNewTalk debug code. It's unreachable since the hook listener itself has a type-hint on user.
- Tweak BeforeEchoEventInsert. It is normal for it to be null for some events, so handle that explicitly and don't treat it as a special case.
- Remove the debug code for AbortEmailNotification, but keep the return true. This should not really happen, but it doesn't hurt to handle it.