Tweak ftdetect stuff

I actually think we don't need to be so smart or fancy with this, and in
fact would prefer to keep it simple.  Just focus on whether they have
the plugin on or not.  I fear adding the autocmd is not very useful and
could have performance implications

Author: amadeus

ftdetect/javascript.vim

@@ -1,14 +1,5 @@
 au BufNewFile,BufRead *.{js,mjs,jsm,es,es6},Jakefile setf javascript
 
-fun! s:SourceFlowSyntax()
-  if !exists('javascript_plugin_flow') && !exists('b:flow_active') &&
-        \ search('\v\C%^\_s*%(//\s*|/\*[ \t\n*]*)\@flow>','nw')
-    runtime extras/flow.vim
-    let b:flow_active = 1
-  endif
-endfun
-au FileType javascript au BufRead,BufWritePost <buffer> call s:SourceFlowSyntax()
-
 fun! s:SelectJavascript()
   if getline(1) =~# '^#!.*/bin/\%(env\s\+\)\?node\>'
     set ft=javascript