fbcode_builder: getdeps: fboss remove OpenNSL manifest
fbcode_builder: getdeps: fboss remove OpenNSL manifest

Summary:
Broadcom has formally replaced OpenNSL with newer OpenNSA:
https://github.com/Broadcom-Network-Switching-Software/OpenNSA/blob/master/README.md

With D16401189, FBOSS no longer depends on OpenNSL, but uses the new OpenNSA
instead. Remove this manifest.

Reviewed By: wez

Differential Revision: D19413708

fbshipit-source-id: f3662f1101d59a5e0e59cb7238797d652564ff90

facebookincubator/mvfst,facebookincubator/mvfst,facebookincubator/mvfst,facebookincubator/mvfst,facebookincubator/mvfst