Revert "Disable mterp for the read barrier config."

Now that cl 196153 is in.

This reverts commit 987e44e6b65677587f37c26e630ddc4d4c563382.

Bug: 26510411
Change-Id: I006d7532973a6e26adde99e04f8b3eab491b3901
diff --git a/runtime/interpreter/interpreter.cc b/runtime/interpreter/interpreter.cc
index e7b4731..6b5218d 100644
--- a/runtime/interpreter/interpreter.cc
+++ b/runtime/interpreter/interpreter.cc
@@ -239,7 +239,7 @@
 }
 
 #if !defined(__clang__)
-#if defined(__arm__) && !defined(ART_USE_READ_BARRIER)
+#if defined(__arm__)
 // TODO: remove when all targets implemented.
 static constexpr InterpreterImplKind kInterpreterImplKind = kMterpImplKind;
 #else
@@ -247,7 +247,7 @@
 #endif
 #else
 // Clang 3.4 fails to build the goto interpreter implementation.
-#if defined(__arm__) && !defined(ART_USE_READ_BARRIER)
+#if defined(__arm__)
 static constexpr InterpreterImplKind kInterpreterImplKind = kMterpImplKind;
 #else
 static constexpr InterpreterImplKind kInterpreterImplKind = kSwitchImplKind;