What I would try to identify which package triggered installation of 32 bit packages:
find a 32-bit package which has been installed as a dependency (
libc6-i386 is a good candidate)
try to uninstall it. If another package depends on it (which should be the case because that's why the library has been installed in the first place), Synaptic will tell you that you need to uninstall that another package as well.
once you uninstalled the package which triggered installation of the 32-bit libs, you can run
sudo apt-get autoremove to remove packages which were installed as dependencies of uninstalled packages.
Similarly, to find all packages which depend on 32-bit libs, try to uninstall, say,
libc6-i386 - this should trigger un-installation of all 32-bit packages in the system.
I'm sure there's also a magic command line one-liner involving dpkg, awk and grep which does the same :)