Don't clear kesytore after 5 auth failures.

Keystore's security originally derived from encrypting keys with a key
derived from the user's password.  To avoid making keystore into a
password brute force oracle, keystore cleared itself after five
incorrect presentations.  All of this has been superseded by moving
keystore's security into Keymaster, and by moving password security
into Gatekeeper/Weaver, and further by implmenting the synthetic
password model.

This CL removes the now-useless and occasionally-dangerous keystore
self-destruct.

Test: Manual
Change-Id: Id85c1c39769701bbc0dcfcb76511faf9eeb65496
2 files changed