Do not remove the k_k until all users are unlocked

The key in keystore is used to encrypt the escrow data. We need to
iterate over all users before deleting it from key store. Otherwise,
the RoR for the 2nd user will fail.

Bug: 172780686
Test: atest CtsAppSecurityHostTestCases:ResumeOnRebootHostTest#resumeOnReboot_TwoUsers_BothUserUnlock_Success
Change-Id: I82d94195fe5716d42e363604be5ead3eb3e300fd