Replace isAdb and enforceShell in DPMS

* Replace isAdb with isAdb(caller)
* Remove enforceShell and use isAdb(caller) instead

Bug: 167960209
Test: atest com.android.server.devicepolicy.DevicePolicyManagerTest
      atest com.android.cts.devicepolicy.MixedDeviceOwnerTest
      atest com.android.cts.devicepolicy.ProfileOwnerTest
      atest com.android.cts.devicepolicy.ManagedProfileTest
Change-Id: Id739a6a41bb647b4e485e1f7a109362874cfb2f0