file isExecutable
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/