Remove a bogus dependency that causes xforms.css not to be generated in srcdir builds.

extensions/xforms/Makefile.in

@@ -135,10 +135,10 @@ EXTRA_DSO_LDOPTS = $(MOZ_COMPONENT_LIBS)
 
 include $(topsrcdir)/config/rules.mk
 
-libs:: xforms.css
+libs::
 	@$(PERL) $(topsrcdir)/config/preprocessor.pl $(DEFINES) $(ACDEFINES) \
-	$^ > $(DIST)/bin/res/xforms.css
+	$(srcdir)/xforms.css > $(DIST)/bin/res/xforms.css
 
-install:: xforms.css
+install::
 	@$(PERL) $(topsrcdir)/config/preprocessor.pl $(DEFINES) $(ACDEFINES) \
-	$^ > $(DESTDIR)$(mozappdir)/res/xforms.css
+	$(srcdir)/xforms.css > $(DESTDIR)$(mozappdir)/res/xforms.css