Clean up how dex preoptimization gets configured.

Change-Id: I505ac438f1b963060b4be36d94bb5fbee6112dc5

core/main.mk

@@ -235,13 +235,15 @@ ifneq (,$(user_variant))
     enable_target_debugging :=
   endif
 
-  # TODO: Remove this and the corresponding block in
-  # config/product_config.make once host-based Dalvik preoptimization is
-  # working.
+  # Turn on Dalvik preoptimization for user builds, but only if not
+  # explicitly disabled and the build is running on Linux (since host
+  # Dalvik isn't built for non-Linux hosts).
   ifneq (true,$(DISABLE_DEXPREOPT))
-  ifeq ($(HOST_OS)-$(WITH_DEXPREOPT_buildbot),linux-true)
-    WITH_DEXPREOPT := true
-  endif
+    ifeq ($(user_variant),user)
+      ifeq ($(HOST_OS),linux)
+        WITH_DEXPREOPT := true
+      endif
+    endif
   endif
 
   # Disallow mock locations by default for user builds

core/product_config.mk

@@ -124,15 +124,6 @@ ifdef product_goals
     default_goal_substitution := tests-build-target
   endif
 
-  # Hack to make the linux build servers use dexpreopt (emulator-based
-  # preoptimization). Most engineers don't use this type of target
-  # ("make PRODUCT-blah-user"), so this should only tend to happen when
-  # using buildbot.
-  # TODO: Remove this once host Dalvik preoptimization is working.
-  ifeq ($(TARGET_BUILD_VARIANT),user)
-    WITH_DEXPREOPT_buildbot := true
-  endif
-
   # Replace the PRODUCT-* goal with the build goal that it refers to.
   # Note that this will ensure that it appears in the same relative
   # position, in case it matters.