If you think it's that file that's responsible, you could reset it back to the packaged defaults by reinstalling the
bash-completion package. We have to be a little more forceful to get it to copy the configuration back, but this should work:
sudo rm /etc/profile.d/bash_completion.sh
sudo apt-get -o Dpkg::Options::="--force-confmiss" install --reinstall bash-completion
Reboot and see where that gets you.
It has just struck me that you might have problems getting to a terminal to enter this! There are several options there but here are my favourite:
They should both set you up as root on your install, and from there you should be able to action a change. If nothing else just delete the current
bash_completion.sh file. That should allow you to log back in normally, albeit without Bash autocompletes.