ASoC: Remove unused dapm_get_snd_card() and dapm_get_soc_card()

These two functions were added two years ago in commit 4805608a

 ("ASoC: dapm -
Add methods to retrieve snd_card and soc_card from dapm context.") but have
remained unused so far. Considering that the dapm context actually has a direct
pointer to the card the functions also seem to be unnecessary. E.g. the
expressions 'dapm_get_soc_card(dapm)' and 'dapm->card' yield the same result.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Mark Brown <broonie@linaro.org>