Remove import as a JS reserved word

[jackfranklin]

Now that JS supports import('/foo.js') it shouldn't be marked as a
reserved word when used in blocks.

This is my first time changing a Vim syntax so apologies if this isn't the right fix - do let me know if you'd like me to make changes. This fixed the problem I was having locally where import was highlighted in red as if it were an error.

[othree]

Hi, thanks for your PR. Your change can fix this issue however I don't expect it solve in this way. I will keep this reserved word and add extra def to over write it in expected context. Actually I have supported import() in another repo: https://github.com/othree/es.next.syntax.vim/blob/master/after/syntax/javascript.vim#L65-L69

This should move to here when it got official support but I forgot to do it. You can help me update the PR to do it.