Summary:
We had to fork OpenNSA and clone from it, see D19437386 for details.
Broadcom has now started hosting OpenNSA as a tarball.
Thus, we no longer need to maintain a fork (yay!)

This patch points opennsa manifest to fetch opennsa from this new location.

Reviewed By: bkoray

Differential Revision: D22175932

fbshipit-source-id: 51cd777ab836e4f191d78fbb2312925e446ca38f