gio: Remove remaining references to fen file monitor

It used to exist on Solaris, but GLib’s support for it was mostly
removed in 2015 in commit 21ab660cf8.

Remove the final few references.

Signed-off-by: Philip Withnall <pwithnall@endlessos.org>

docs/reference/gio/meson.build

@@ -4,7 +4,6 @@ if get_option('gtk_doc')
 
   ignore_headers = [
     'fam',
-    'fen',
     'gdbus-2.0',
     'gvdb',
     'inotify',

docs/reference/gio/overview.xml

@@ -392,7 +392,7 @@ Gvfs is also heavily distributed and relies on a session bus to be present.
         The #GFileMonitor implementation for local files that is included
         in GIO on Linux has the name <literal>inotify</literal>, others that are built
         are built as modules (depending on the platform) are called
-        <literal>fam</literal> and <literal>fen</literal>.
+        <literal>fam</literal>, <literal>kqueue</literal> and <literal>win32filemonitor</literal>.
       </para><para>
         The special value <literal>help</literal> can be used to print a list of
         available implementations to standard output.