Fixed user leave problem on private chat, close #3799 HTML5

...on-html5/imports/api/users/server/modifiers/removeUser.js

bigbluebutton-html5/imports/api/users/server/publishers.js

...luebutton-html5/imports/startup/server/userPermissions.js

bigbluebutton-html5/imports/ui/components/chat/container.jsx

...ponents/chat/message-list/message-list-item/component.jsx

bigbluebutton-html5/imports/ui/components/chat/service.js

...ton-html5/imports/ui/components/user-avatar/component.jsx

...uebutton-html5/imports/ui/components/user-list/service.js