Delete / Finalize Vaults

[0xbigz]

sharing thoughts on topic raise by both @dannpl and @wphan

• easy to support if vault.total_shares = 0 and vault.init_ts - now > MIN_VAULT_LIFETIME, then let anyone close out vault (and associated user account through cpi call)
• force closure, when these invariants above aren't true, seems more difficult/complex
• ensuring that vault.total_shares can get to 0 (rather than dust) should be examined during testing