Tweaked new message indicator calculation: (#4763)

* Removed count from new message indicator

* Don't count deleted posts towards the unviewedCount

* remove lodash, reduce() is natively available

webapp/components/post_view/components/new_message_indicator.jsx

@@ -40,7 +40,7 @@ export default class NewMessageIndicator extends React.Component {
                     />
                     <FormattedMessage
                         id='posts_view.newMsgBelow'
-                        defaultMessage='{count} new {count, plural, one {message} other {messages}} below'
+                        defaultMessage='New {count, plural, one {message} other {messages}} below'
                         values={{count: this.props.newMessages}}
                     />
                 </div>

webapp/components/post_view/components/post_list.jsx

@@ -1,6 +1,5 @@
 // Copyright (c) 2015 Mattermost, Inc. All Rights Reserved.
 // See License.txt for license information.
-
 import $ from 'jquery';
 
 import Post from './post.jsx';
@@ -84,13 +83,15 @@ export default class PostList extends React.Component {
         // Only count if we're  not at the bottom, not in highlight view,
         // or anything else
         if (nextProps.scrollType === Constants.ScrollTypes.FREE) {
-            for (let i = order.length - 1; i >= 0; i--) {
-                const post = posts[order[i]];
+            unViewedCount = order.reduce((count, orderId) => {
+                const post = posts[orderId];
                 if (post.create_at > nextProps.lastViewedBottom &&
-                    post.user_id !== nextProps.currentUser.id) {
-                    unViewedCount++;
+                    post.user_id !== nextProps.currentUser.id &&
+                    post.state !== Constants.POST_DELETED) {
+                    return count + 1;
                 }
-            }
+                return count;
+            }, 0);
         }
         this.setState({unViewedCount});
     }