mfd: cros_ec: Remove unused __remove function

This function is no longer called, so we get a harmless
warning until it is removed as well:

drivers/mfd/cros_ec_dev.c:265:13: error: '__remove' defined but not used [-Werror=unused-function]

Fixes: 3aa2177e ("mfd: cros_ec: Use devm_kzalloc for private data")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Lee Jones <lee.jones@linaro.org>