Set recents policy to default on session close.

This ensures that any automated apps will show in the default device's
recents once the session terminates.

Bug: 437848392
Test: atest ComputerControlSessionTest
Flag: android.companion.virtualdevice.flags.computer_control_access
Change-Id: I5a7301b45f11cfe581451dd9ac4c26bd5a5ce2af