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.cryptfile. When I try to login, the CLI just crashes with an
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.