MM-22051: Remove ToJson from model (part 1) (#18005)

https://mattermost.atlassian.net/browse/MM-22051

```release-note
Removed the following methods/functions:
(ad *AccessData) ToJson()
(ar *AccessResponse) ToJson()
(ar *AnalyticsRow) ToJson()
(ar AnalyticsRows) ToJson()
(o *Audit) ToJson()
(o Audits) ToJson()
(ad *AuthData) ToJson()
(ar *AuthorizeRequest) ToJson()
(o *ChannelPatch) ToJson()
(o *ChannelsWithCount) ToJson()
(o *ChannelCounts) ToJson()
(o *ChannelData) ToJson()
(o *ChannelMembers) ToJson()
(o *ChannelUnread) ToJson()
(o *ChannelUnreadAt) ToJson()
(o *ChannelStats) ToJson()
(o *ChannelView) ToJson()
(o *ChannelViewResponse) ToJson()
(o *ClusterDiscovery) ToJson()
(ci *ClusterInfo) ToJson()
(cs *ClusterStats) ToJson()
(o *Command) ToJson()
CommandListToJson(l []*Command) string
(o *CommandArgs) ToJson()
(cmr *CommandMoveRequest) ToJson()
(o *CommandResponse) ToJson()
(c *Compliance) ToJson()
(c Compliances) ToJson()
(o *Config) ToJson()
EmojiListToJson(emojiList []*Emoji)
```

web/oauth.go

@@ -240,7 +240,9 @@ func getAccessToken(c *Context, w http.ResponseWriter, r *http.Request) {
 	auditRec.Success()
 	c.LogAudit("success")
 
-	w.Write([]byte(accessRsp.ToJson()))
+	if err := json.NewEncoder(w).Encode(accessRsp); err != nil {
+		mlog.Warn("Error writing response", mlog.Err(err))
+	}
 }
 
 func completeOAuth(c *Context, w http.ResponseWriter, r *http.Request) {