Remove a message that tells whether a user exists

[msimkunas]

This PR removes a message that tells the client whether a user with a given email address exists on the system.

[bennothommo]

@msimkunas I'm assuming this is to stop people from being able to work out which accounts exist on a site or not (user enumeration).

Does this change result in no flash message being shown if the user does not exist? If there's a flash message shown if the user does exist, this will just provide another avenue of enumeration - watch to see if a flash message is thrown.

Ideally, we should be throwing a flash message no matter if the user exists or not, saying something along the lines of "If your account exists, you will receive an email shortly with instructions on resetting your password". This prevents people from being able to work out if the user exists based solely on the message provided. (Ideally, we should also be queueing the email sent as well so that people can't use timing to work out if the user exists or not from the delay of an email being sent).

[msimkunas]

@bennothommo I've updated the partial text and changed Mail::send to Mail::queue so that emails are queued.

[LukeTowers]

@bennothommo LGTM, will let you do the merge once you're happy :)