ASoC: samsung: remove last traces of neo1973-gta01

The support for the Openmoko Neo1973 GTA01 got removed in commit
1ae5cbc5 ("ASoC: neo1973_wm8753:
remove references to the neo1973-gta01 machine"). Remove its last traces
in the Kconfig file too.

Signed-off-by: Paul Bolle <pebolle@tiscali.nl>
Acked-by: Kukjin Kim <kgene.kim@samsung.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>