MAINTAINERS: Drop Andreas as 0.15 maintainer

Downgrade to orphan status, like all other remaining stable entries.
Signed-off-by: NAndreas Färber <afaerber@suse.de>

MAINTAINERS

@@ -1399,9 +1399,8 @@ S: Orphan
 
 Stable 0.15
 L: qemu-stable@nongnu.org
-M: Andreas Färber <afaerber@suse.de>
 T: git git://git.qemu-project.org/qemu-stable-0.15.git
-S: Supported
+S: Orphan
 
 Stable 0.14
 L: qemu-stable@nongnu.org