Hi,
Your message should better been posted on english forums...
I clearly believe it's a bad idea to install a plugin not updated since more than 4 years, on a Moodle version not indicated as supported, and really hope you didn't installed directly on a production server, but on a test server first... if not, you're clearly doing all that should be avoided!!!
You don't indicate how you tried to install it, and when you have this message (and if it's for everybody or just you).
You should certainly be able to delete the corresponding directory on the server, to delete this plugin...
Your message should better been posted on english forums...
I clearly believe it's a bad idea to install a plugin not updated since more than 4 years, on a Moodle version not indicated as supported, and really hope you didn't installed directly on a production server, but on a test server first... if not, you're clearly doing all that should be avoided!!!
You don't indicate how you tried to install it, and when you have this message (and if it's for everybody or just you).
You should certainly be able to delete the corresponding directory on the server, to delete this plugin...
And Moodle 4.0 directly integrates an ability to notify participants of new/updated resources/activities 
HTH,
Séverin
Séverin