X.L.Fullscreen: Silence deprecation warning temporarily

Deprecation warnings are now shown to users via xmessage when xmonad
recompiles, and this may include warnings in xmonad(-contrib) itself if
people have a build script that invokes stack/cabal without --silent,
and they then may get confused. The deprecation warning in that case
won't be shown every recompile but only once whenever xmonad(-contrib)
needs to be rebuilt, but it's still annoying.

This silences the warning. We intend to refactor this part of the code
so this is a temporary measure.

Fixes: f666cf4e4e0e ("X.H.EwmhDesktops: Deprecate standalone hooks")

XMonad/Layout/Fullscreen.hs

@@ -1,4 +1,5 @@
 {-# LANGUAGE FlexibleContexts, MultiParamTypeClasses, FlexibleInstances #-}
+{-# OPTIONS_GHC -Wno-deprecations #-} -- FIXME: fullscreenStartup temporarily silenced
 -----------------------------------------------------------------------------
 -- |
 -- Module      :  XMonad.Layout.Fullscreen