Hey there,
If I understand your question correctly, do you mean that you want to disable the emojis at the composer editor? (Kindly refer the screenshot)
If yes, It is impossible to do that in the backend setting currently.
In order to disable the emojis at the composer editor, you need to modify the settings.js file.
You can just download the attached settings.js file and placed it at your original file. JoomlaFolder/administrator/components/com_easydiscuss/themes/default/structure/settings.js
We will consider it to add the setting in the next version release.