Remove duplication, split tests

The code move to libdexfile/dex/descriptors_names.cc apparently did not
remove the original code from runtime/utils.cc.  Fix that duplication
and all the header mentions needed.  Also, split the test files to go
along with the new locations for the code to be tested.

Bug: 22322814
Test: make -j 50 checkbuild
      make -j 50 test-art-host-gtest
      flash & boot marlin

Change-Id: Ie734672c4bca2c647d8016291f910b5608674545
diff --git a/dex2oat/dex2oat.cc b/dex2oat/dex2oat.cc
index b5c5e45..37d1317 100644
--- a/dex2oat/dex2oat.cc
+++ b/dex2oat/dex2oat.cc
@@ -59,6 +59,7 @@
 #include "debug/elf_debug_writer.h"
 #include "debug/method_debug_info.h"
 #include "dexlayout.h"
+#include "dex/descriptors_names.h"
 #include "dex/dex_file-inl.h"
 #include "dex/quick_compiler_callbacks.h"
 #include "dex/verification_results.h"