PLT-4200/3708 Fixed outside team DM switching, allowed switching to uncreated DMs (#4111)

* Fixed outside team DM switching, allowed switching to uncreated DMs

* Update channel_switch_modal.jsx

webapp/utils/utils.jsx

@@ -1032,13 +1032,6 @@ export function getDirectChannelName(id, otherId) {
     return handle;
 }
 
-export function getDirectChannelNameByUsername(username, otherUsername) {
-    const id = UserStore.getProfileByUsername(username).id;
-    const otherId = UserStore.getProfileByUsername(otherUsername).id;
-
-    return getDirectChannelName(id, otherId);
-}
-
 // Used to get the id of the other user from a DM channel
 export function getUserIdFromChannelName(channel) {
     var ids = channel.name.split('__');