Revert "Write dex files to oat file early."

This reverts commit 625a64aad13905d8a2454bf3cc0e874487b110d5.

Breaks the Mac build:

Undefined symbols for architecture i386:
  "_CloseArchive", referenced from:
      ... in oat_writer.o
ld: symbol(s) not found for architecture i386

Change-Id: I21608bc51437834e1e6abde9bcbe5e7d9998197e
diff --git a/runtime/runtime.cc b/runtime/runtime.cc
index 5b075b7..c4694ee 100644
--- a/runtime/runtime.cc
+++ b/runtime/runtime.cc
@@ -1131,14 +1131,10 @@
     }
 
     std::vector<std::unique_ptr<const DexFile>> boot_class_path;
-    if (runtime_options.Exists(Opt::BootClassPathDexList)) {
-      boot_class_path.swap(*runtime_options.GetOrDefault(Opt::BootClassPathDexList));
-    } else {
-      OpenDexFiles(dex_filenames,
-                   dex_locations,
-                   runtime_options.GetOrDefault(Opt::Image),
-                   &boot_class_path);
-    }
+    OpenDexFiles(dex_filenames,
+                 dex_locations,
+                 runtime_options.GetOrDefault(Opt::Image),
+                 &boot_class_path);
     instruction_set_ = runtime_options.GetOrDefault(Opt::ImageInstructionSet);
     std::string error_msg;
     if (!class_linker_->InitWithoutImage(std::move(boot_class_path), &error_msg)) {