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/post.go

@@ -114,7 +114,7 @@ func (a *App) CreatePost(post *model.Post, channel *model.Channel, triggerWebhoo
 		!post.IsSystemMessage() &&
 		channel.Name == model.DEFAULT_CHANNEL &&
 		!CheckIfRolesGrantPermission(user.GetRoles(), model.PERMISSION_MANAGE_SYSTEM.Id) {
-		return nil, model.NewLocAppError("createPost", "api.post.create_post.town_square_read_only", nil, "")
+		return nil, model.NewAppError("createPost", "api.post.create_post.town_square_read_only", nil, "", http.StatusForbidden)
 	}
 
 	// Verify the parent/child relationships are correct