Policy change PGP storage warning is misleading

When running `keybase login` today I was confronted with this message about the passphrase policy change:

``` text
Policy change on passphrases

We've gotten lots of feedback that it's annoying as all hell to enter a
Keybase passphrase after restarts and updates. The consensus is you can
trust a device's storage to keep a secret that's specific to that device.
Passphrases stink, like passed gas, and are bloody painful, like passed stones.

Note, however: on this device you have a PGP private key in Keybase's local
keychain. Some people want to type a passphrase to unlock their PGP key, and
this new policy would bypass that. If you're such a person, you can run the
following command to remove your PGP private key.

keybase pgp purge

If you do it, you'll have to use GPG for your PGP operations.

If you're ok with the new policy, you can run this command so you won't
get bothered with this message in the future:

keybase dismiss pgp-storage

Thanks!
```

This message makes it sound as though by running `keybase pgp purge` I can make it so that using my PGP private key(s) requires a passphrase. However, I've determined that I can still use my private keys when I have a network connection because the CLI uses my session with the Keybase API to decrypt and sign using my stored PGP keys.

It may be that the intersection of folks who want to have to use their passphrase to unlock their PGP key and folks who upload their PGP key is small, but I thought this was surprising behavior that isn't clear from the messaging of the policy change text.

Start by reproducing the warning during `keybase login`, then compare the stated effects of `keybase pgp purge` with actual use of the stored PGP key while online and offline. The work is done when the warning accurately describes the resulting key and passphrase behavior, or the behavior is corrected to match the message.

Written by the indexing model from the issue text.