Remove lang bundles included by vim-polyglot

Remove the following lang bundles because they are already
included in sheerun/vim-polyglot:

* othree/html5.vim
* tpope/vim-markdown
* tpope/vim-haml
* pangloss/vim-javascript
* kchmck/vim-coffee-script
* groenewege/vim-less
* StanAngeloff/php.vim