Enable dexpreopt for `arm_v7_v8`.

Host tests fail if host boot images are missing.

Test: m test-art-host-gtest
Change-Id: Ibb3a1d09e515e0d5ae1f7e3456059b3c6bbfa752
diff --git a/arm_v7_v8/BoardConfig.mk b/arm_v7_v8/BoardConfig.mk
index e30e784..c5618f5 100644
--- a/arm_v7_v8/BoardConfig.mk
+++ b/arm_v7_v8/BoardConfig.mk
@@ -30,7 +30,3 @@
 
 TARGET_SUPPORTS_32_BIT_APPS := true
 TARGET_SUPPORTS_64_BIT_APPS := true
-
-
-# Disable dexpreopt for an unbundled ART build.
-WITH_DEXPREOPT := false