Fix `resetEncryption` to remove secrets in 4S (#4683)
* fix(crypto): `resetEncryption` remove secrets in 4S
Remove the cross signing keys and the backup decryption key of the 4S when calling `resetEncryption`
* test(crypto): expect secrets to be deleted in 4S when `resetEncryption` is called
* test(secret storage): add test case when the secret is set at null
* fix(crypto): remove default key in 4S
* test(crypto): default key should be removed from 4S
