Make missing DEX2OAT_TARGET_INSTRUCTION_SET_FEATURES an error

Change-Id: I3ca23e4db80c8ab8a86da6408cf38daccd4cfaf1
diff --git a/dex2oat/dex2oat.cc b/dex2oat/dex2oat.cc
index 1472337..5b0653e 100644
--- a/dex2oat/dex2oat.cc
+++ b/dex2oat/dex2oat.cc
@@ -632,13 +632,9 @@
   CompilerBackend compiler_backend = kQuick;
 #endif
 
-  // Take the default set of instruction features from the build if present.
+  // Take the default set of instruction features from the build.
   InstructionSetFeatures instruction_set_features =
-#ifdef ART_DEFAULT_INSTRUCTION_SET_FEATURES
-    ParseFeatureList(STRINGIFY(ART_DEFAULT_INSTRUCTION_SET_FEATURES));
-#else
-    ParseFeatureList("default");
-#endif
+      ParseFeatureList(STRINGIFY(ART_DEFAULT_INSTRUCTION_SET_FEATURES));
 
 #if defined(__arm__)
   InstructionSet instruction_set = kThumb2;