KeyChain: Remove Screenlock dependency

In coordination with KeyChain changes, stop using FLAG_ENCRYPTED when
importing keys into KeyStore and remove the requirement that a screen
lock is present.

The change to this package removes the checks for KeyStore state and
Keyguard presence. See the KeyChain change for more detailed
explanation.

Test: atest CtsDevicePolicyManagerTestCases:com.android.cts.devicepolicy.MixedProfileOwnerTest#testKeyManagement
Bug: 120901345
Change-Id: I82f1c18e84dd4a63d55017fa4b7be31c45f7ef14