Remove unportable use of "system rm"

#

# 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'";