If you wish to delete or remove a plugin do the following:
Open File Explorer
Navigate to \Documents\My IDEA Documents\Local Library\Macros.ILB\IDEA Lab
Double click the Remove.exe file of the plugin you wish to remove.
Select Yes to confirm you wish to remove it.
Note. – Once the plugin has been removed you must close IDEA and reopen it in order for it to be removed from the ribbon.