office-js: added mailbox.removeHandlerAsync
office-js: added mailbox.removeHandlerAsync

dsebastien/DefinitelyTyped,magny/DefinitelyTyped,magny/DefinitelyTyped,georgemarshall/DefinitelyTyped,dsebastien/DefinitelyTyped,georgemarshall/DefinitelyTyped,markogresak/DefinitelyTyped,mcliment/DefinitelyTyped,borisyankov/DefinitelyTyped,georgemarshall/DefinitelyTyped,borisyankov/DefinitelyTyped,georgemarshall/DefinitelyTyped