Back out 7286dac15291 (bug 820148) since it doesn't work

build/Makefile.in

@@ -57,12 +57,6 @@ APP_INI_DEPS += $(DEPTH)/config/buildid
 
 DEFINES += -DGRE_MILESTONE=$(GRE_MILESTONE) -DAPP_BUILDID=$(APP_BUILDID)
 
-# Set a flag that can be used in pref files to disable features if
-# we are not building for Aurora or Nightly.
-ifeq (,$(findstring a,$(GRE_MILESTONE)))
-PREF_PPFLAGS += -DRELEASE_BUILD
-endif
-
 DEFINES += -DMOZ_APP_VERSION="$(MOZ_APP_VERSION)"
 APP_INI_DEPS += $(DEPTH)/config/autoconf.mk