Removed unnecessary <GhMembersListItem> backing class

no issue

- `ember-moment` provides the `{{moment-from-now}}` helper that does the same thing the `.memberSince` computed property was doing

app/components/gh-members-list-item.hbs

@@ -31,7 +31,7 @@
 
         <LinkTo @route="member" @model={{@member}} title="Member details" class="gh-list-data gh-members-list-subscribed-at gh-list-cellwidth-20 nowrap middarkgrey f8 {{if (not @member.name) "gh-members-subscribed-noname"}}">
             {{#if @member.createdAtUTC}}
-                {{moment-format @member.createdAtUTC "MMM DD, YYYY"}} <span class="midlightgrey">({{this.memberSince}})</span>
+                {{moment-format @member.createdAtUTC "MMM DD, YYYY"}} <span class="midlightgrey">({{moment-from-now @member.createdAtUTC}})</span>
             {{/if}}
         </LinkTo>
 

app/components/gh-members-list-item.js

@@ -1,13 +0,0 @@
-import Component from '@glimmer/component';
-import moment from 'moment';
-
-export default class GhMembersListItemComponent extends Component {
-    get memberSince() {
-        // member can be a proxy in a sparse array so .get is required
-        let createdAt = this.args.member.get('createdAtUTC');
-        if (createdAt) {
-            return moment(createdAt).from(moment());
-        }
-        return null;
-    }
-}