Do not link last-edited timestamp to annotation single view

Render, but do not link, the last-edited timestamp. Having both this
and the created timestamp linked to the single-annotation view can lead
to confusion, as it might seem like they link to two different places
if they’re both linked.

src/sidebar/components/annotation-header.js

@@ -44,7 +44,6 @@ function AnnotationHeader({
                 (edited{' '}
                 <Timestamp
                   className="annotation-header__timestamp-edited-link"
-                  href={annotationLink}
                   timestamp={annotation.updated}
                 />
                 ){' '}

src/styles/sidebar/components/annotation-header.scss

@@ -21,8 +21,7 @@
     color: $grey-4;
   }
 
-  &__timestamp-created-link,
-  &__timestamp-edited-link {
+  &__timestamp-created-link {
     &:hover {
       text-decoration: underline;
     }
@@ -32,10 +31,6 @@
     color: $grey-5;
   }
 
-  &__timestamp-edited-link {
-    color: $grey-4;
-  }
-
   &__highlight {
     margin-right: 5px;
   }