Remove unused length from DexFile GetString calls.

Address extra review comments from commit
dfb325e0ddd746cd8f7c2e3723b3a573eb7cc111.

Change-Id: If76e81e7af5870431901de0bf561e0f827435fe3
diff --git a/runtime/native/dalvik_system_VMRuntime.cc b/runtime/native/dalvik_system_VMRuntime.cc
index 71ed95c..aef000c 100644
--- a/runtime/native/dalvik_system_VMRuntime.cc
+++ b/runtime/native/dalvik_system_VMRuntime.cc
@@ -221,8 +221,7 @@
     return;
   }
   const DexFile* dex_file = dex_cache->GetDexFile();
-  uint32_t utf16Size;
-  const char* utf8 = dex_file->StringDataAndUtf16LengthByIdx(string_idx, &utf16Size);
+  const char* utf8 = dex_file->StringDataByIdx(string_idx);
   string = strings[utf8];
   if (string == NULL) {
     return;