Keystore2: Stop using WAL mode

WAL mode attempts to open an additional file for use as a shared memory
mechanism. If storage is too full, then the database fails to open.
Remove the use of WAL mode so that keystore can perform read-only
transactions on the database and startup even on a full disk.

Disabling WAL mode shows about a 5% performance drop on a synthetic test
that creates and destroys 5000 AES keys.

Bug: 190142197
Test: keystore2_test
Change-Id: I9b1cb7e6398e07fa9f02f0ba4e9eb48313c06472
Merged-In: I9b1cb7e6398e07fa9f02f0ba4e9eb48313c06472
3 files changed