Pass the verify flag to DexFileLoader utilities.

Refactoring-only change.

Also remove unused DexFilerLoader::OpenMemory.

bug: 30972906
bug: 63920015

Test: build.

Change-Id: I7cd4b5787565ab1a3457ce2be6bb14657229c550
diff --git a/runtime/dex2oat_environment_test.h b/runtime/dex2oat_environment_test.h
index a9bb954..57cef3d 100644
--- a/runtime/dex2oat_environment_test.h
+++ b/runtime/dex2oat_environment_test.h
@@ -84,6 +84,7 @@
     std::vector<std::unique_ptr<const DexFile>> multi1;
     ASSERT_TRUE(DexFileLoader::Open(GetMultiDexSrc1().c_str(),
                                     GetMultiDexSrc1().c_str(),
+                                    /* verify */ true,
                                     kVerifyChecksum,
                                     &error_msg,
                                     &multi1)) << error_msg;
@@ -92,6 +93,7 @@
     std::vector<std::unique_ptr<const DexFile>> multi2;
     ASSERT_TRUE(DexFileLoader::Open(GetMultiDexSrc2().c_str(),
                                     GetMultiDexSrc2().c_str(),
+                                    /* verify */ true,
                                     kVerifyChecksum,
                                     &error_msg,
                                     &multi2)) << error_msg;