ASoC: audio-graph-card2: remove Experimental announce

Audio Graph Card2 has been announcing "Audio Graph Card2 is
still under Experimental stage", but it is time to remove it.
This patch removes it.

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Link: https://lore.kernel.org/r/87k042nm6s.wl-kuninori.morimoto.gx@renesas.com


Signed-off-by: Mark Brown <broonie@kernel.org>