Fix ground combat to report defending land units

Fix ground combat to report defending land units

Commit 092a52f2 (v4.3.4) removed the code to estimate defense, because
the use of the estimate had been disabled since v4.0.0.  This
accidentally removed the reporting of defending units, because
get_dlist() reported them when called for an estimate, and not when
called for real.

Fix by removing the unused estimate capability from get_dlist().  It
now reports defending units always.
(cherry picked from commit 64f44e99044a8b28b8631a27fc882a959f737f84)