iwlwifi: mvm: remove code that stops multiple UMAC scans of a type

We can only have one scan per type at the same time, so the code that
tries to stop several scans of a type is unnecessary.  Remove that to
reduce code complexity.

Signed-off-by: Luciano Coelho <luciano.coelho@intel.com>
Reviewed-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>