Finally do away with NewLocAppError function. (#7498)

This cleans up the few NewLocAppError calls that crept in since the main
bulk of them were removed, and finally removes the NewLocAppError
function altogether.

app/webhook.go

@@ -522,7 +522,7 @@ func (a *App) HandleIncomingWebhook(hookId string, req *model.IncomingWebhookReq
 
 	if utils.IsLicensed() && *utils.Cfg.TeamSettings.ExperimentalTownSquareIsReadOnly &&
 		channel.Name == model.DEFAULT_CHANNEL {
-		return model.NewLocAppError("HandleIncomingWebhook", "api.post.create_post.town_square_read_only", nil, "")
+		return model.NewAppError("HandleIncomingWebhook", "api.post.create_post.town_square_read_only", nil, "", http.StatusForbidden)
 	}
 
 	if channel.Type != model.CHANNEL_OPEN && !a.HasPermissionToChannel(hook.UserId, channel.Id, model.PERMISSION_READ_CHANNEL) {