ASoC: Remove unnecessary device_remove_file()

Since commit d29697dc ("ASoC: Add sysfs entries via static attribute
groups") the sysfs attributes of the rtd are manged by the device core and
there is no need to manually call device_remove_file() anymore.

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