pci-hotplug-old: Has been dead for five major releases, bury

Commit 79ca616 (v1.6.0) accidentally disabled legacy x86-only HMP
commands pci_add, pci_del: it defined CONFIG_PCI_HOTPLUG only as make
variable, not as preprocessor macro, killing the code conditional on
defined(CONFIG_PCI_HOTPLUG_OLD).

In all this time, nobody reported the loss.  I only noticed it when I
tried to test some error reporting change that forced me to touch this
old crap again.

Fun: git-log hw/pci/pci-hotplug-old.c shows our faith in the backward
compatibility god has been strong enough to sacrifice at its altar
about a dozen times, but not strong enough to even once verify the
legacy feature's still there, let alone works.

Remove the commands along with the code backing them.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

stubs/Makefile.objs

@@ -24,7 +24,6 @@ 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-y += pci-drive-hot-add.o
 stub-obj-$(CONFIG_SPICE) += qemu-chr-open-spice.o
 stub-obj-y += qtest.o
 stub-obj-y += reset.o

stubs/pci-drive-hot-add.c

@@ -1,10 +0,0 @@
-#include <monitor/monitor.h>
-#include <sysemu/sysemu.h>
-#include <sysemu/blockdev.h>
-
-int pci_drive_hot_add(Monitor *mon, const QDict *qdict, DriveInfo *dinfo)
-{
-    /* On non-x86 we don't do PCI hotplug */
-    monitor_printf(mon, "Can't hot-add drive to type %d\n", dinfo->type);
-    return -1;
-}