Remove old Esperanto character conversion support

Remove old Esperanto character conversion support

Deletes LanguageEo.php class which only had remains of the server-side
character conversion (sx <-> ŝ, etc). This is being obsoleted in favor
of client-side IMEs provided by UniversalLanguageSelector extension.

Removes deprecated $wgEditEncoding, which was only used for this.

Turns Language::recodeInput() and Language::recordForEdit() into no-ops
for any old or extension code that happened to still use them.

Bug: T62677
Change-Id: Ib647353538d258dee941f2f7c571191060bc9c7d