Remove all of the current smiley support as it currently isn't used and needs to be completely overhauled for the new emoji api when we write it.

Testing Done:
Ran the unit tests, `ninja pidgin-pot doc`, ran pidgin3, opened the preferences page, verified the `custom smileys menu was removed`, sent messages over xmpp with text smileys and verified that pidgin 2 still rendered them.

Reviewed at https://reviews.imfreedom.org/r/852/