Rework pool versions index/diff views

- Changed to using the diff-body CSS class
-- Removed unneeded CSS style file
- Removed trailing whitespace after the >>> link
-- It was causing artifact line-throughs to appear after the link
- Changed the diff link to only render when a text field has changed
-- Because the post changes are already shown on the index view
- Specifically add <br> to statuses to cause line breaks

app/javascript/src/styles/specific/pool_versions.scss

@@ -1,17 +0,0 @@
-div#c-pool-versions {
-  #a-diff {
-    del {
-      background: var(--wiki-page-versions-diff-del-background);
-      text-decoration: none;
-    }
-
-    ins {
-      background: var(--wiki-page-versions-diff-ins-background);
-      text-decoration: none;
-    }
-
-    span.paragraph-mark {
-      opacity: 0.25;
-    }
-  }
-}