Revert "Clear #filetypeplugin for filetype-based ODL (#24)"

This reverts commit 1d477a1a01390f8aa122d9cdb30a44ba469d2253.
Ensure ftplugin files are loaded (#24)

If `filetype plugin on` is called before `plug#end()`, filetype
plugin handler is invoked before ODL autocmd from vim-plug which
updates runtimepath and ftplugin files are not loaded.