Remove /boot partition

You could use cp -a /boot /boot-tmp to copy the contents to a temporary directory on the root filesystem, unmount the boot partition using umount /boot, and put the files back in place with rmdir /boot && mv /boot-tmp /boot.

Once you verify that everything is fine you can remove /boot from /etc/fstab. Finally, you should double-check the GRUB configuration and run update-grub.

You could also just keep the /boot partitition and expand it with gparted. (Of course, as always, backup first and keep a liveCD handy in case something goes wrong)

If you've never resized partitions before, there are plenty of tutorials on the web that will tell you how to do it. Here's a good tutorial to start with: http://www.ibm.com/developerworks/linux/library/l-resizing-partitions-1/index.html