If you can reboot and get to the (repair Filesystem)# prompt, I think (and I'm going from memory here) that your mounted filesystem is still your initrd.
If your root filesystem is on LVM, you need to do a few things. (If it's not this won't work. Let me know if that's the case.)
First, you need to pvscan, vgscan, possibly vgchange -ay, then lvscan to see if the logical volumes are available. If running off the initial ramdisk filesystem, those commands aren't directly available. You have to 'lvm pvscan', 'lvm vgscan', etc.
When you get to the point where the 'lvm lvscan' shows your root filesystem logical volume is active, you can mount it and edit /etc/fstab.
So you could "mkdir /m", 'mount /dev/<volumegroup>/<rootlogicalvolume> /m', then 'vi /m/etc/fstab' to remove the offending line. Reboot and you should be ok.
This is all from memory, so I hope my recall is good. Good luck. Post your results, good or bad.