iwlwifi: dvm: remove Kconfig default

The split of iwlwifi into DVM and MVM was a long time ago now,
so we can remove the "default IWLWIFI" that we had to keep all
existing .config files with working defaults during the split.
This is no longer necessary, practically nobody should now be
upgrading a .config that's older than the split.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>