Fix hack incompatibility with cryptfile keyring

I'm not exactly sure what this hack was ever supposed to accomplish, but it's clearly unnecessary for dummy keyrings like keyrings.alt or keyrings.cryptfile. When I try to login, the CLI just crashes with an AttributeError on keyring.backend.get_all_keyring.__wrapped__.always_returns, which is what the hack is trying to remove anyway.

So this patch just skips trying to del the attribute if it already doesn't exist.