Replace MergeSets() with std::set::merge().

And clear up ownership of the VerifierDeps being merged
by using std::unique_ptr<>.

Test: m test-art-host-gtest
Test: testrunner.py --host
Bug: 123750182
Change-Id: Id4ffa9f9fa1968fa762b9e825f25827240f6d45d
6 files changed