Remove support for non-threaded VNC server

QEMU now has a fundamental requirement for pthreads, so there
is no compelling reason to retain support for the non-threaded
VNC server. Remove the --{enable,disable}-vnc-thread configure
arguments, and all CONFIG_VNC_THREAD conditionals

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
diff --git a/ui/Makefile.objs b/ui/Makefile.objs
index 3687c8a..adc07be 100644
--- a/ui/Makefile.objs
+++ b/ui/Makefile.objs
@@ -4,11 +4,7 @@
 vnc-obj-y += vnc-enc-zrle.o
 vnc-obj-$(CONFIG_VNC_TLS) += vnc-tls.o vnc-auth-vencrypt.o
 vnc-obj-$(CONFIG_VNC_SASL) += vnc-auth-sasl.o
-ifdef CONFIG_VNC_THREAD
-vnc-obj-y += vnc-jobs-async.o
-else
-vnc-obj-y += vnc-jobs-sync.o
-endif
+vnc-obj-y += vnc-jobs.o
 
 common-obj-y += keymaps.o
 common-obj-$(CONFIG_SPICE) += spice-core.o spice-input.o spice-display.o