mu4e-maildir-shortcuts: update for today's functionality

The text:

  Optionally, you can add the following:
  `:hide'  - if t, maildir is hdden from the main-view and speedbar.
  `:hide-unread' - do not show the counts of unread/total number
  of messages for the maildir in the main-view.

is not true for the current version, so let's remove it.

*

mu4e/mu4e-vars.el

@@ -574,11 +574,6 @@ Each of the list elements is a plist with at least:
 `:maildir'  - the maildir for the shortcut (e.g. \"/archive\")
 `:key'      - the shortcut key.
 
-Optionally, you can add the following:
-`:hide'  - if t, maildir is hdden from the main-view and speedbar.
-`:hide-unread' - do not show the counts of unread/total number
- of messages for the maildir in the main-view.
-
 For backward compatibility, an older form is recognized as well:
 
    (maildir . key), where MAILDIR is a maildir (such as