Refactor Dex open methods

Consolidate dex opening around a simpler single interface in DexFile.
Making this change prior to moving all but the simplest interface out of
dex_file.{cc,h}.

Bug: 22322814
Change-Id: I4c55019912a19a1c90f9022c20f5b8b954fc7a47
Test: test-art-{host,target}
diff --git a/runtime/dex_file_verifier_test.cc b/runtime/dex_file_verifier_test.cc
index 71c0ad9..5939ef3 100644
--- a/runtime/dex_file_verifier_test.cc
+++ b/runtime/dex_file_verifier_test.cc
@@ -123,7 +123,7 @@
 class DexFileVerifierTest : public CommonRuntimeTest {
  protected:
   DexFile* GetDexFile(const uint8_t* dex_bytes, size_t length) {
-    return new DexFile(dex_bytes, length, "tmp", 0, nullptr, nullptr);
+    return new DexFile(dex_bytes, length, "tmp", 0, nullptr);
   }
 
   void VerifyModification(const char* dex_file_base64_content,