The installation instructions state:
To use it, firstly install wmctrl
:
sudo apt-get install wmctrl
Then, download the archive from here, extract it and double click
the "desktop-indicator.py" file.
To add Desktop Indicator to startup, search for "Startup Applications"
in Dash (or access it via the session menu - top right icon), click
"Add", under "Name" enter "Desktop Indicator" and under "Command"
click "Browse" and select "desktop-indicator.py" from where you've
extracted the downloaded archive.
Therefore to remove the indicator - at a minimum, would be to remove the application you have added via "Startup Applications" i.e.
search for "Startup Applications" in Dash (or access it via the session menu - top right icon), highlight "Desktop Indicator" and click the remove button.
Logout and login.