gio: Remove fam file monitor support

libgamin was last released in 2007 and is dead
[upstream](https://gitlab.gnome.org/Archive/gamin). Distributions may
still ship it (although Fedora no longer does), but we want people to
use inotify on Linux since it’s actively supported.

BSDs use kqueue. Windows uses win32filemonitor.

FAM might still be used on some commercial Unix distributions, but there
are no contributors from those distributions, and certainly no CI for
them to prevent regressions.

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

Fixes: #2614

docs/reference/gio/meson.build

@@ -3,7 +3,6 @@ if get_option('gtk_doc')
   subdir('xml')
 
   ignore_headers = [
-    'fam',
     '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>, <literal>kqueue</literal> and <literal>win32filemonitor</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.
@@ -665,7 +665,7 @@ Gvfs is also heavily distributed and relies on a session bus to be present.
       </para>
       <para>
         GIO uses this extension point internally, to switch between
-        its fam-based and inotify-based file monitoring implementations.
+        its kqueue-based and inotify-based file monitoring implementations.
       </para>
    </formalpara>