MDL-40045 auth: removed unnecessary add_to_log calls

Both LDAP and Shibboleth call complete_user_login which triggers
a user_loggedin event that handles the legacy call to add_to_log.
MDL-40045 auth: introduced PHPUnit test to ensure logging in via LDAP triggers an event
MDL-40045 user: replaced add_to_log call when a user profile is viewed with an event
MDL-40045 user: replaced add_to_log call when the user list is viewed with an event
MDL-40045 login: replaced add_to_log call when a user updates their password with an event