Fix _distance in dze_buildChecks

Passing false as the second parameter to fnc_find_plots always returns
DZE_PlotPole select 0. In dze_buildchecks we want to use DZE_PlotPole
select 1 if the classname is a plot pole.

_distance is already defined as DZE_PlotPole select 0 in the other three
files, so it is redundant to redefine it as the return value.

In player_upgrade.sqf the check for DZE_permanentPlot is not necessary,
because FNC_check_access handles both cases.

SQF/dayz_code/actions/player_buildingDowngrade.sqf

@@ -15,7 +15,6 @@ _needText = localize "str_epoch_player_246";
 _playerUID = [player] call FNC_GetPlayerUID;
 _canBuildOnPlot = false;
 _plotcheck = [player, false] call FNC_find_plots;
-_distance = _plotcheck select 0;
 _IsNearPlot = _plotcheck select 1;
 _nearestPole = _plotcheck select 2;