ninja is not a virus, it is a build system like
However, you have built and installed an indicator that is not finished or ready for use. Github is not an application store, and you should not install things off there unless you understand what you are doing and trust the developer. In fact, you should not run any commands you find anywhere on the internet without understanding what they do first.
To uninstall it, run the following from the same directory that you ran the commands to install the indicator:
sudo ninja uninstall
ninja, the tool you used to install the indicator to remove any files it installed when you ran
sudo ninja install