removed icon stack from email area of helpgrid

lms/static/sass/_discussion.scss

@@ -1432,6 +1432,7 @@ body.discussion {
 
   .helpgrid-row-notification {
     .icon-sign-blank {color: $green;}
+    .icon-envelope {color: $gray;}
   }
 
   .discussion-article {

lms/templates/discussion/index.html

@@ -86,10 +86,7 @@
 		        		<li class="helpgrid-row helpgrid-row-notification">
 		        			<span class="row-title">Receive updates</span>
 		        			<div class="row-item-full">
-								<span class="icon-stack">
-									<i class="icon-sign-blank icon-stack-base"></i>
-									<i class="icon-envelope icon-light"></i>
-								</span>
+		        				<i class="icon icon-envelope"></i>
 								<span class="row-setting"><input type="checkbox" name="email-notification"></input></span>
 								<span class="row-description"> If enabled, you will receive an email digest if there is new activity from posts you are following. </span>
 							</div>