Remove oat file location in the image.

The oat file is now always in the same directory, and has the
same name as the image file. Only difference is the extension.

This also removes the need for host-prefix.

Change-Id: I16d1f7aeb1d58372d41921694664e9c321afc1ad
diff --git a/runtime/native/dalvik_system_DexFile.cc b/runtime/native/dalvik_system_DexFile.cc
index 1a3ceb8..8a96d79 100644
--- a/runtime/native/dalvik_system_DexFile.cc
+++ b/runtime/native/dalvik_system_DexFile.cc
@@ -285,7 +285,7 @@
           ScopedObjectAccess soa(env);
           LOG(INFO) << "DexFile_isDexOptNeeded cache file " << cache_location
               << " has out-of-date oat checksum compared to "
-              << image_header.GetImageRoot(ImageHeader::kOatLocation)->AsString()->ToModifiedUtf8();
+              << oat_file->GetLocation();
         }
         return JNI_TRUE;
       }
@@ -295,7 +295,7 @@
           ScopedObjectAccess soa(env);
           LOG(INFO) << "DexFile_isDexOptNeeded cache file " << cache_location
               << " has out-of-date oat begin compared to "
-              << image_header.GetImageRoot(ImageHeader::kOatLocation)->AsString()->ToModifiedUtf8();
+              << oat_file->GetLocation();
         }
         return JNI_TRUE;
       }