MAINTAINERS: Remove and change David Gilbert maintainer entries

I'm leaving Red Hat next week, so clean up the maintainer entries.

'virtiofs' is just the device code now, so is pretty small, and
Stefan is still a maintainer there.

'migration' still has Juan.

For 'HMP' I'll swing that over to my personal email.

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Acked-by: Dr. David Alan Gilbert <dave@treblig.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Reviewed-by: Zhang Chen <chen.zhang@intel.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Message-id: 20230330095524.37691-1-dgilbert@redhat.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

MAINTAINERS

@@ -2119,7 +2119,6 @@ T: git https://github.com/borntraeger/qemu.git s390-next
 L: qemu-s390x@nongnu.org
 
 virtiofs
-M: Dr. David Alan Gilbert <dgilbert@redhat.com>
 M: Stefan Hajnoczi <stefanha@redhat.com>
 S: Supported
 F: hw/virtio/vhost-user-fs*
@@ -2863,7 +2862,7 @@ F: tests/unit/test-rcu-*.c
 F: util/rcu.c
 
 Human Monitor (HMP)
-M: Dr. David Alan Gilbert <dgilbert@redhat.com>
+M: Dr. David Alan Gilbert <dave@treblig.org>
 S: Maintained
 F: monitor/monitor-internal.h
 F: monitor/misc.c
@@ -3136,7 +3135,6 @@ F: scripts/checkpatch.pl
 
 Migration
 M: Juan Quintela <quintela@redhat.com>
-M: Dr. David Alan Gilbert <dgilbert@redhat.com>
 S: Maintained
 F: hw/core/vmstate-if.c
 F: include/hw/vmstate-if.h