Drop effectively unused kemoticons support

Summary:
Konversation only supported emoticons if config value EnableEmotIcons
was true. This by default was false and there is no UI for configuring
this, making it effectively unused.

This appears to be deliberate from the code comments.

This helps clear up some KEmoticon library usage for future KF6
transitioning.

UTF-8 emoticons work correctly.

Test Plan: Compiles

Differential Revision: https://phabricator.kde.org/D24000