iwlwifi: mvm: remove multiple debugfs entries

Now that we have per station control over amsdu size no need for
multiple entries, especially that the old one is misleading due to not
setting it for all protocols as a limit.

Signed-off-by: Mordechay Goodstein <mordechay.goodstein@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>