fix(invite): do not show caret in input (#2774)

react/features/base/react/components/web/MultiSelectAutocomplete.js

             <div>
                 <MultiSelectStateless
                     filterValue = { this.state.filterValue }
+                    icon = { null }
                     isDisabled = { isDisabled }
                     isLoading = { this.state.loading }
                     isOpen = { this.state.isOpen }