build: Fix 'make dist' regression

Commit f084b60377 incorrectly set
DIST_SUBDIRS for the toplevel Makefile.am.  In general actually we
don't need to set it, because modern automake automatically sets
it by looking at conditionals for SUBDIRS.

Tested-by: Rico Tzschichholz <ricotz@t-online.de>

https://bugzilla.gnome.org/show_bug.cgi?id=667806

gio/Makefile.am

@@ -2,7 +2,6 @@ include $(top_srcdir)/Makefile.decl
 
 NULL =
 
-DIST_SUBDIRS =
 SUBDIRS = gdbus-2.0/codegen
 
 if OS_UNIX
@@ -328,8 +327,6 @@ endif
 
 if BUILD_MODULAR_TESTS
 SUBDIRS += tests 
-else
-DIST_SUBDIRS += tests
 endif
 
 libgio_2_0_la_SOURCES =		\

glib/Makefile.am

@@ -36,15 +36,11 @@ MAYBE_PCRE = pcre
 endif
 
 SUBDIRS = libcharset $(PRINTF_SUBDIR) $(MAYBE_PCRE) update-pcre .
-DIST_SUBDIRS =
+DIST_SUBDIRS = libcharset gnulib pcre update-pcre tests
 if BUILD_MODULAR_TESTS
 SUBDIRS += tests 
-else
-DIST_SUBDIRS += tests
 endif
 
-DIST_SUBDIRS = libcharset gnulib pcre update-pcre tests
-
 AM_CPPFLAGS = 				\
 	$(glib_INCLUDES) 		\
 	$(pcre_inc) 			\

gobject/Makefile.am

@@ -5,11 +5,8 @@
 include $(top_srcdir)/Makefile.decl
 
 SUBDIRS = .
-DIST_SUBDIRS =
 if BUILD_MODULAR_TESTS
 SUBDIRS += tests 
-else
-DIST_SUBDIRS += tests
 endif
 
 BUILT_SOURCES=