Switch x86_64 emulator to 64 bit primary.

Also siezes the opportunity to remove the hardcoded
TARGET_PREFER_32_BIT_APPS directing in core_64_bit.mk.
This avoids the need for further hacks but needs supporting
changes to a few apps to force them to 32 bit.

Change-Id: I36ba9e5f5b08dd87d6a4afc27961a436306eed99
diff --git a/CleanSpec.mk b/CleanSpec.mk
index 7108e10..c64f316 100644
--- a/CleanSpec.mk
+++ b/CleanSpec.mk
@@ -223,6 +223,10 @@
 # Unset TARGET_PREFER_32_BIT_APPS for 64 bit targets.
 $(call add-clean-step, rm -rf $(PRODUCT_OUT)/system/build.prop)
 
+# Switching the x86 emulator over to a 64 bit primary zygote.
+$(call add-clean-step, rm -rf $(PRODUCT_OUT)/system/build.prop)
+$(call add-clean-step, rm -rf $(PRODUCT_OUT)/root/default.prop)
+
 # ************************************************
 # NEWER CLEAN STEPS MUST BE AT THE END OF THE LIST
 # ************************************************