Replace DM logic in view_start_chat_or_reuse

Part of https://github.com/vector-im/riot-web/issues/10416

This code is used by the welcome bot logic and the groups/communities section of the app. goHomeOnCancel can be removed because no matter what happens we'll end up in a room with the user (and we aren't showing a dialog anymore).

src/components/structures/GroupView.js

@@ -343,7 +343,6 @@ const FeaturedUser = React.createClass({
         dis.dispatch({
             action: 'view_start_chat_or_reuse',
             user_id: this.props.summaryInfo.user_id,
-            go_home_on_cancel: false,
         });
     },