[CLEANUP] stats: use stksess_kill() to remove table entries

Using it will be more reliable in the long term as we'll only have
to modify stksess_kill() if we want to extend the tables.
diff --git a/src/dumpstats.c b/src/dumpstats.c
index a6ce0cf..526e0f5 100644
--- a/src/dumpstats.c
+++ b/src/dumpstats.c
@@ -546,10 +546,7 @@
 				return 1;
 			}
 
-			eb32_delete(&ts->exp);
-			ebmb_delete(&ts->key);
-			stksess_free(&px->table, ts);
-
+			stksess_kill(&px->table, ts);
 			/* end of processing */
 			return 1;
 		}