This variable was used for development purposes and was accidentally
introduced in
https://github.com/kubernetes/kubernetes/commit/f0f78299348afcf770d4e8d89dcea82f80811b28.

This is its only use in the tree:
https://github.com/kubernetes/kubernetes/search?q=USE_RELEASE_NODE_BINARIES&unscoped_q=USE_RELEASE_NODE_BINARIES