Render account verified icon using CSS

As mentioned in commit 925f04e3f, icon classes make screen readers
announce strange symbols and aren't properly displayed for people who
have changed their preferred font family.

app/assets/stylesheets/account/verify-account.scss

@@ -2,14 +2,13 @@
   padding-right: $line-height / 2;
 
   .already-verified {
+    @include has-fa-icon(check, solid);
     color: $check;
     line-height: $line-height * 2;
 
-    .icon-check {
+    &::before {
       color: $text-medium;
-      font-size: rem-calc(24);
-      line-height: rem-calc(45);
-      vertical-align: middle;
+      font-size: 1.4em;
     }
   }
 }

app/components/account/verify_account_component.html.erb

@@ -1,7 +1,6 @@
 <div class="verify-account">
   <% if account.level_three_verified? %>
     <p class="already-verified">
-      <span class="icon-check"></span>
       <%= t("account.show.verified_account") %>
     </p>
   <% else %>