MAINTAINERS: remove or downgrade myself to reviewer from some subsystems

MAINTAINERS: remove or downgrade myself to reviewer from some subsystems

Other people are doing a much better work than myself at handling some
subsystems.  For those files it is better if I downgrade myself to
reviewer or recognize that I am not actually doing any work there.

Cc: Daniel P. Berrange <berrange@redhat.com>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Cc: Eric Blake <eblake@redhat.com>
Cc: Thomas Huth <thuth@redhat.com>
Cc: Laurent Vivier <lvivier@redhat.com>
Cc: Marc-André Lureau <marcandre.lureau@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>