qemu.test.watchdog: Remove RHEL.5 from the ib700 cfg

Remove RHEL.5 from the cfg, sinece RHEL.5 not support ib700wdt.

Signed-off-by: Yunping Zheng <yunzheng@redhat.com>
Merge pull request #1365 from humanux/watchdog

qemu.test.watchdog: Remove RHEL.5 from the ib700 cfg