qerror: Finally unused, clean up

Remove it except for two things in qerror.h:

* Two #include to be cleaned up separately to avoid cluttering this
  patch.

* The QERR_ macros.  Mark as obsolete.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Luiz Capitulino <lcapitulino@redhat.com>

stubs/Makefile.objs

@@ -21,7 +21,6 @@ stub-obj-y += machine-init-done.o
 stub-obj-y += migr-blocker.o
 stub-obj-y += mon-is-qmp.o
 stub-obj-y += mon-printf.o
-stub-obj-y += mon-set-error.o
 stub-obj-y += monitor-init.o
 stub-obj-y += notify-event.o
 stub-obj-$(CONFIG_SPICE) += qemu-chr-open-spice.o

stubs/mon-is-qmp.c

@@ -1,6 +1,8 @@
 #include "qemu-common.h"
 #include "monitor/monitor.h"
 
+Monitor *cur_mon;
+
 bool monitor_cur_is_qmp(void)
 {
     return false;

stubs/mon-set-error.c

@@ -1,8 +0,0 @@
-#include "qemu-common.h"
-#include "monitor/monitor.h"
-
-Monitor *cur_mon;
-
-void monitor_set_error(Monitor *mon, QError *qerror)
-{
-}