The second section is not necessary as long as you can boot the newer kernel without issue and as long as the system is stable while running the new kernel. Once you've determined that all is well you can go ahead and remove those lines.
Any time there is a kernel update you will find that the boot stanza for the new kernel has been added to the existing boot configuration.
as glennzo stated, it's not really necessary, but I would keep it there just in case something does get messed up in your current kernel and you need to boot up a different one.
yum, by default, will keep the last 3 kernels (and the entries in your /boot/grub/grub.conf file) so that you can boot previous kernels in case of problems.
Linear Mode
