iwlwifi: pcie: remove some dead code

We can never get into this code with a gen2/3 device, and therefore
don't need to allocate the byte count tables in a single contiguous
DMA region. Just WARN and bail out if something is misconfigured.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Link: https://lore.kernel.org/r/iwlwifi.20200425130140.a748d33252ef.If2f5810016efb40b041f93fe8c6b4c251542e2f1@changeid