Emoji are the ideograms or smileys 😃 used in electronic messages and Web pages. Originating in Japan on mobile devices, they are now commonly available on devices worldwide, ranging from mobile to desktop computers.
Different operating systems have distinct methods of accessing emoji. Note that these methods work in most applications, not just WordPress. Read more on WordPress.org
Most websites are not need to load WordPress emojis, therefore Swift Performance provides a option to disable them. You can simply enable Disable Emojis option in settings to remove them from WordPress