Remove !g_thread_supported() codepaths in gio

In particular, remove the libasyncns import, which was only used by
GUnixResolver, which is only used when threads are not available.
Likewise remove GWin32Resolver, and the hacky broken non-threaded
parts of GIOScheduler.

https://bugzilla.gnome.org/show_bug.cgi?id=616754

gio/Makefile.am

@@ -5,7 +5,7 @@ NULL =
 SUBDIRS = gdbus-2.0/codegen
 
 if OS_UNIX
-SUBDIRS += libasyncns xdgmime
+SUBDIRS += xdgmime
 endif
 
 if OS_WIN32_AND_DLL_COMPILATION
@@ -200,8 +200,8 @@ endif
 
 if OS_UNIX
 appinfo_sources += gdesktopappinfo.c
-platform_libadd += libasyncns/libasyncns.la xdgmime/libxdgmime.la
-platform_deps += libasyncns/libasyncns.la xdgmime/libxdgmime.la
+platform_libadd += xdgmime/libxdgmime.la $(RESOLVER_LIBADD)
+platform_deps += xdgmime/libxdgmime.la
 unix_sources = \
 	gfiledescriptorbased.c  \
 	gunixconnection.c	\
@@ -211,8 +211,6 @@ unix_sources = \
 	gunixmount.c		\
 	gunixmount.h		\
 	gunixmounts.c 		\
-	gunixresolver.c		\
-	gunixresolver.h		\
 	gunixsocketaddress.c	\
 	gunixvolume.c 		\
 	gunixvolume.h 		\
@@ -241,8 +239,6 @@ endif
 win32_actual_sources = \
 	gwin32mount.c \
 	gwin32mount.h \
-	gwin32resolver.c \
-	gwin32resolver.h \
 	gwin32volumemonitor.c \
 	gwin32volumemonitor.h \
 	gwin32inputstream.c \