Remove potential double free

Janis noticed that GetAuthTokenKey has ownership retained by the
implementer, but the caller in libgatekeeper is delete[]ing it.

Bug: 120610663
Test: gatekeeper-unit-tests, Gatekeeper 1.0 VTS against Trusty
Change-Id: I67171d707706b1ebe5caad47447762144495e28b
1 file changed