iwlwifi: remove unused DC2DC_CONFIG_CMD definitions

We haven't used this command for a long time, if ever, so we can
remove all related definitions.

Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Link: https://lore.kernel.org/r/iwlwifi.20220130115024.26c0044110cc.Ie0d215a22618e7a3ecc39eca349914981b608b4d@changeid
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>