Attempt to unlink session file if hardlink fails

If either creating the link or changing the file permissions fails, the session
should clean up the link so that a fallback manual copy can succeed. This can occur
during APEX rollback.

Bug: 274802935

Test: manual, follow steps in bug to test rollback mechanism

Change-Id: Ic15bbe657a11a26b4bbcc48dca2f3e3a3f1239e2