Remove remnant verto screensharing and use kurento instead.

bigbluebutton-client/resources/prod/lib/kurento-extension.js

bigbluebutton-client/resources/prod/lib/verto-min.js

bigbluebutton-client/resources/prod/lib/verto_extension.js

...button/modules/screenshare/managers/ScreenshareManager.as

...on/modules/screenshare/managers/WebRTCDeskshareManager.as

...ton/modules/screenshare/utils/WebRTCScreenshareUtility.as

...rc/org/bigbluebutton/modules/users/views/UsersWindow.mxml