Remove stephpy/vim-yaml syntax

It causes issues:
- https://github.com/dracula/vim/pull/163
- https://github.com/stephpy/vim-yaml/issues/22

after/ftplugin/yaml.vim

@@ -1,11 +0,0 @@
-if !exists('g:polyglot_disabled') || index(g:polyglot_disabled, 'yaml-extras') == -1
-
-" Vim indent file
-" Language: Yaml
-" Author: Henrique Barcelos
-" Date: 2014-10-08
-" URL: https://github.com/hjpbarcelos
-setlocal autoindent sw=2 ts=2 expandtab
-" vim:set sw=2:
-
-endif