ASoC: codecs: wm0010: remove unused struct 'wm0010_spi_msg'

'wm0010_spi_msg' has been unused since the original
commit e3523e01

 ("ASoC: wm0010: Add initial wm0010 DSP driver").

Remove it.

Signed-off-by: Dr. David Alan Gilbert <linux@treblig.org>
Reviewed-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Link: https://msgid.link/r/20240601225446.183505-3-linux@treblig.org
Signed-off-by: Mark Brown <broonie@kernel.org>