Revert "notification text for comment"

This reverts commit 363bf09a6e8af952bb83ad461cd9f735b4416909.

lib/util/slack.js

@@ -134,9 +134,6 @@ module.exports = function(crowi) {
     if (updateType == 'create') {
       text = `:white_check_mark: ${user.username} created a new page! ${pageUrl}`;
     }
-    else if (updateType == 'comment') {
-      text = `:speech_balloon: ${user.username} commented on ${pageUrl}`;
-    }
     else {
       text = `:up: ${user.username} updated ${pageUrl}`;
     }