datadog-agent: remove privateTmp=true

This allows postgres integration to connect to socket in /tmp

(cherry picked from commit 5715aa1)
Signed-off-by: Domen Kožar <domen@dev.si>

nixos/modules/services/monitoring/datadog-agent.nix

@@ -213,7 +213,6 @@ in {
           Group = "datadog";
           Restart = "always";
           RestartSec = 2;
-          PrivateTmp = true;
         };
         restartTriggers = [ datadogPkg ] ++ map (etc: etc.source) etcfiles;
       } attrs;