[Facades] Fix tarball (for real this time)

Turns out EXTRA_DISTFILES only works with library.make or executable.make,
so we need to just use DISTFILES here...

mcs/class/Facades/Makefile

@@ -29,7 +29,7 @@ include $(MCS_BUILD_DIR)/rules.make
 dist-local: dist-default
 
 DIST_SUBDIRS = $(net_4_x_PARALLEL_SUBDIRS)
-EXTRA_DISTFILES=subdirs.make
+DISTFILES=subdirs.make
 
 doc-update-local:
 	@echo "not doing docs"