gatekeeper: fix new[]/delete mismatch

UniquePtr<T[]> uses delete[], whereas UniquePtr<T> uses delete. Since
we're using new[], we should be using delete[].

Caught by clang's static analyzer.

Bug: 27101951
Test: mma. Static analyzer warning is gone.
Change-Id: I30a72b8c111764f602aeee7c09fc2ce781ad58cb
1 file changed