Stop purging caches in bin/storage adjust

Summary:
Fixes T6548.

• This workflow doesn't work under reasonable configurations and isn't trivial to fix (see T6548).
• We don't need it; this just makes things a little bit faster if you have to migrate everything (e.g., immediately after T1191) and the installs we know about have generally upgraded by now.
• This keeps kicking PKCS8 keys out of cache which is a pain.

Test Plan: Ran bin/storage adjust without it doing an implicit cache purge.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T6548

Differential Revision: https://secure.phabricator.com/D11377