Revert "stream: add an API to make streams do blocking writes"

This reverts commit 92040eb7123e892261c8da71c3eedb97c00e4b88.

I haven't even attempted to compile this, I will do so later today. Just wanted to gather comments from you guys.

AFAICT this is not used anywhere, doesn't have a test and doesn't work as advertised.

Of course, I could be totally wrong here.

/cc @piscisaureus @indutny