registration: Enable copying profile settings in production.

Now that we've styled this feature properly, this makes it possible to
copy various user-preferences type profile data in production when
making a new account with the same email address as an existing
account.

zerver/lib/users.py

@@ -183,8 +183,6 @@ def access_user_by_id(user_profile: UserProfile, user_id: int,
     return target
 
 def get_accounts_for_email(email: str) -> List[Dict[str, Optional[str]]]:
-    if settings.PRODUCTION:  # nocoverage
-        return []
     profiles = UserProfile.objects.select_related('realm').filter(delivery_email__iexact=email.strip(),
                                                                   is_active=True,
                                                                   is_bot=False,