wpsimpletools

Completely disables comments functionality from backend and frontend: 
* Hides existing comments 
* Close comments on the front-end 
* Disable support for comments, trackbacks and ping 
* Redirects any user trying to access comments page 
* Removes comments metabox from dashboard 
* Removes comments links from admin bar 
* Removes comments page in menu 
* Completely disables comments API

Disable Comments

The type of plugin I just love... does exactly what it says, no configuration necessary, source readable and understandable in minutes.

Simple, effective, no config ✅

Completely disables comments functionality from backend and frontend. Just install it, nothing to configure!

shmider

A small and easy to use plugin for removing pending comments using search keyword. 
Yes, there is no need to go into the database, just set a keyword and all the comments contains that keyword will be deleted. 
You can also get the number of pending comments contain the keyword before actually removing them.

WP Comments Remover

A small plugin to remove pending comments using a search keyword.

Disable Comments vs WP Comments Remover