Zeroize weaverSecret in unlockLskfBasedProtector()

Secrets derived from or unlocked by the LSKF need to be zeroized as soon
as they are no longer needed.

Test: atest FrameworksServicesTests:com.android.server.locksettings
Bug: 320392352
Bug: 395976735
Flag: EXEMPT bugfix
Change-Id: I391533ae3eb5d56f687bb18d64aceb7b309cde67