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
diff --git a/dexlayout/dex_verify.cc b/dexlayout/dex_verify.cc
index 718d66f..83a7c69 100644
--- a/dexlayout/dex_verify.cc
+++ b/dexlayout/dex_verify.cc
@@ -22,6 +22,8 @@
 
 #include <inttypes.h>
 
+#include <set>
+
 #include "android-base/stringprintf.h"
 
 namespace art {