Reuse the same salt to compute recoverablekeystore snapshot.

Salt is updated after LSKF change.
Verified that database upgrade and downgrade work prooerly.

atest com.android.server.locksettings.recoverablekeystore
Test: manual
Flag: EXEMPT flagging this change adds complexity and increases risk of
mistakes.
Bug: 428975093

Change-Id: I030dbf815fa759c2cd794b8ad6289254db87070a