Revert "Sign future releases"

This reverts commit 1457e0bd9a5ea68b1c301a8ce2890c77e5e78df7.
Bundler caches gems even when bundling from a GitHub repository, so the
lack of a private key breaks Inflections for anybody who wants to bundle
via :github.

Signed-off-by: David Celis <me@davidcel.is>