iwlwifi: mvm: fix "failed to remove key" message

When the GTK is installed, we install it to HW with the
station ID of the AP.

Mac80211 will try to remove it only after the AP sta is
removed, which will result in a failure to remove key
since we do not have any station for it.

This is a valid situation, but a previous commit removed
the early return and added a return with error value, which
resulted in an error message that is confusing to users.

Remove the error return value.

Fixes: 85aeb58c ("iwlwifi: mvm: Enable security on new TX API")
Signed-off-by: Sara Sharon <sara.sharon@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>