Remove old code to support multiple images

Change-Id: I29bc2f216361ac4ed0cc0fefb7e3c46ee64e0ae8
diff --git a/src/runtime.h b/src/runtime.h
index 8a86c3c..e34a577 100644
--- a/src/runtime.h
+++ b/src/runtime.h
@@ -63,7 +63,7 @@
     std::string boot_class_path_;
     std::string class_path_;
     std::string host_prefix_;
-    std::vector<std::string> images_;
+    std::string image_;
     bool check_jni_;
     std::string jni_trace_;
     bool is_compiler_;