Remove most font-awesome references in CSS

Most of the references were fontAwesome SVG icons that we'd hacked
directly in to the CSS for some reason I forget. No longer needed.

`.notification__message .fa` just becomes `.notification-group__icon
.icon`; it's for changing the color of the little "the following message in
your notification is a Follow notification" icon to be an on-theme color.
Changed the target so it still works.

Got rid of some styling for a haml template that doesn't exist anymore.

Notably I'm leaving in some `.fa` references because they are still in
Mastodon! Probably a bug I'll file with them.

https://github.com/mastodon/mastodon/blob/v4.5.1/app/javascript/styles/mastodon/widgets.scss#L50-L65

app/javascript/styles/hometown.scss

@@ -44,15 +44,6 @@
   display: none;
 }
 
-// app/views/statuses/_simple_status.html.haml
-// Set width and height for the local-only indicator
-.status__action-bar-button.icon-button:has(.fw.fa-chain-broken) {
-  font-size: 18px;
-  width: 23.1429px;
-  height: 23.1429px;
-  line-height: 23.15px;
-}
-
 // app/javascript/mastodon/features/compose/components/poll_form.jsx
 // Add some custom styling for the "multiple choice" selection button
 .compose-form__poll-wrapper .is-multiple-toggle {