iwlwifi: mvm: remove unused field in iwl_mvm_tid_data

Commit 69c7fda4 removed the
users of iwl_mvm_tid_data.reduced_tpc. Due to a conflict,
I forgot to commit the hunk that removed the field itself.
Do this know.

Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>