I had the same issue and solve it following the steps in the next link: How to completely uninstall/remove a package/software/program.
That helped me removing all and only the dependencies/packages that were installed with the sudo apt-get install lubuntu-desktop command.
Edit:
I'll try to guide you better.
First of all, if you followed @Saurav instructions, I'd recommend to install lubuntu-desktop again so we make sure all deleted packages are in your system.
When I used the previous command, a bunch of new packages/programs were to be installed along. To show a few:

and the list goes on...
To get rid of all these, you should use
sudo apt-get remove --auto-remove abiword abiword-common ... etc
listing every package installed. To do so, we are gonna find all these packages in the history.log file, which keeps a record of all APT installations, upgrades or removals. Open the log file with the following:
gedit /var/log/apt/history.log
Here, use Ctrl+F to search the term "lubuntu-desktop" and you should see something like this:

Note: If you don't find the command here, as it happened to me, the log file has been rotated. Go to /var/log/apt/ with nautilus /var/log/apt/, double-click history.log.1.gz and open history.log.1 (look the name of the gedit tab in the previous image).
Now, select all the packages until the "End-Date: 2014 ..." line, copy and paste them in a new gedit file. As you can see, these packages are in the form "package_name:i386 (something between parenthesis)". Note that "i386" could be "amd64" depending on your OS. Now, from what we've got, only the package name is important. To remove the extra stuff, press Ctrl+H to invoke the find & replace tool. In the Search for input field, type (again, depending on your OS):
:i386 \([0-9\:\~\.\+a-zA-Z\-, ]*\),?
:amd64 \([0-9\:\~\.\+a-zA-Z\-, ]*\),?
Leave the Replace with field blank, check coincide regular expression and press Replace all.

Now, you have the list of installed packages separated by space, so copy them, open up your terminal and type:
sudo apt-get remove --auto-remove *paste packages*
And that's it. You have completely removed lubuntu-desktop
Regards,