dist-upgrade to install Elementary DE. By doing so, you installed PPA provided versions of packages over standard Ubuntu versions. For example, if Ubuntu provides a
nautilus package, and those PPAs provide another
nautilus package with higher version, you installed that one.
That's why only removing extra elementary packages such as
elementary-icon-themes is not sufficient. You have to remove those patched packages too!
So, to completely remove elementary effect, you must go back to Ubuntu versions of packages. To do so, you need
ppa-purge. Because only (as a tool to do these things)
ppa-purge downgrade packages from PPA versions to Ubuntu versions.
Use these (Change the list according to your usage of PPAs)
sudo ppa-purge ppa:elementary-os/daily
sudo ppa-purge ppa:elementary-os/os-patches
sudo ppa-purge ppa:elementary-os/testing
sudo ppa-purge ppa:mpstark/elementary-tweaks-daily
sudo ppa-purge ppa:elementary-os/stable
To completely get rid of elementary things.
If you don't have
ppa-purge already installed, install using
sudo apt-get install ppa-purge
Note 1: If you already removed those PPA repository either using
sudo apt-add-repository -r or manually editing files, re-add them. Because
ppa-purge needs those package list to do the downgrading. After re-adding them, use
sudo apt-get update
command to refresh package index.
Note 2: If you are having an error from
ppa-purge saying it can't find
sudo apt-get install aptitude
to install it.
Note 3: If
ppa-purge fails for some PPAs not being available, remove those PPA entries manually.
ppa-purge won't work if every repository doesn't work.
Note 4: If some of PPAs are disabled now (after installing package from them), you have little luck downgrading them automatically. You can identify them and manually downgrade them using synaptic or aptitude. But it's a tedious job.
Note 5: If you still see Elementary session listed on Lightdm, remove
pantheon-session package manually.
Notes 6: Remove every extra packages you can identify installed from those PPAs but not available in Ubuntu repositories.