fixes #439 exposing nn_sleep() was a mistake

Revert "fixes #437 inconsistent DLL linkage for nn_sleep"
This reverts commit 3d978156c04bd75052deaa1726f2b4b5bccc989c.

Revert "Allowed nn_sleep to be exported on Windows."
This reverts commit e3588bc987f60fa841c153df89a70c7a3f1eb02c.
7 files changed