Revert "Fixed DPMS.setDeviceOwner() permission check."

That change broke `dpm set-device-owner` on headless system user
because when the identiy was cleared, 'isAdb()` would return false.

Test: atest com.android.cts.devicepolicy.MixedDeviceOwnerTest#testDelegation
Bug: 200810234

This reverts commit 1b7f9845.

Change-Id: Ie12a58466af5fbfd834478aec98e0aef9384121f