Two solutions:
Remove the plugin through the list of installed plugins
(the illustrations are from the blog post "Install Eclipse UI Form Editor" written by Albert ATTARD):
The "about eclipse" menu will give you access to the list of installed Software:
You can click on the right application (m2eclipse for you, Jiglo in this example), and click uninstall, and restart eclipse.
A safer solution would be first to install a new fresh copy of Eclipse, and add your existing plugins (except m2eclipse): if that fails, you still have your previous Eclipse installation untouched.
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…