Remove unportable use of "system rm"

mysql-test/t/ps.test

@@ -1168,9 +1168,6 @@ deallocate prepare stmt2;
 #
 # CREATE TABLE with DATA DIRECTORY option
 #
-# Protect ourselves from data left in tmp/ by a previos possibly failed
-# test
---system rm -f $MYSQLTEST_VARDIR/tmp/t1.*
 --disable_warnings
 --disable_query_log
 eval prepare stmt from "create table t1 (c char(10)) data directory='$MYSQLTEST_VARDIR/tmp'";