Revert "ARM: VIXL32: Use VIXL backend by default."

Revert while investigating.

bug:35977033

This reverts commit e6316892821287b1d1906b9962eae129fbdc37be.

Change-Id: I51e24a6e539072a6d0d470dfe41855a4847f3e96
diff --git a/compiler/optimizing/code_generator_arm_vixl.h b/compiler/optimizing/code_generator_arm_vixl.h
index 3f52c72..8ae3b7d 100644
--- a/compiler/optimizing/code_generator_arm_vixl.h
+++ b/compiler/optimizing/code_generator_arm_vixl.h
@@ -35,11 +35,11 @@
 #include "aarch32/macro-assembler-aarch32.h"
 #pragma GCC diagnostic pop
 
-// Default to use the VIXL-based backend on ARM.
-#ifdef ART_USE_OLD_ARM_BACKEND
-static constexpr bool kArmUseVIXL32 = false;
-#else
+// True if VIXL32 should be used for codegen on ARM.
+#ifdef ART_USE_VIXL_ARM_BACKEND
 static constexpr bool kArmUseVIXL32 = true;
+#else
+static constexpr bool kArmUseVIXL32 = false;
 #endif
 
 namespace art {