drop CLOBBER bits, otherwise make complains ?

Index: Makefile.in
--- Makefile.in.orig
+++ Makefile.in
@@ -49,20 +49,10 @@ ifndef TEST_MOZBUILD
 ifndef MOZ_PROFILE_USE
 # We need to explicitly put BUILD_BACKEND_FILES here otherwise the rule in
 # rules.mk doesn't run early enough.
-$(TIERS) binaries:: CLOBBER $(BUILD_BACKEND_FILES)
+$(TIERS) binaries:: $(BUILD_BACKEND_FILES)
 endif
 endif
 
-ifdef JS_STANDALONE
-.PHONY: CLOBBER
-CLOBBER:
-else
-CLOBBER: $(topsrcdir)/CLOBBER
-	@echo 'STOP!  The CLOBBER file has changed.'
-	@echo 'Please run the build through "mach build".'
-	@exit 1
-endif
-
 install_manifests := \
   $(addprefix dist/,branding idl include public private xpi-stage) \
   _tests \
@@ -75,7 +65,6 @@ ifeq (,$(filter FasterMake+RecursiveMake,$(BUILD_BACKE
 install_manifests += dist/bin
 endif
 install_manifest_depends = \
-  CLOBBER \
   $(BUILD_BACKEND_FILES) \
   $(NULL)
 
