9p: some more cleanup in #include directives

The "9p-attr.h" header isn't needed by 9p synth and virtio 9p.

While here, also drop last references to virtio from 9p synth since it is
now transport agnostic code.

Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>

hw/9pfs/9p-synth.c

 /*
- * Virtio 9p synthetic file system support
+ * 9p synthetic file system support
  *
  * Copyright IBM, Corp. 2011
  *
@@ -13,9 +13,7 @@
  */
 
 #include "qemu/osdep.h"
-#include "hw/virtio/virtio.h"
 #include "9p.h"
-#include "9p-xattr.h"
 #include "fsdev/qemu-fsdev.h"
 #include "9p-synth.h"
 #include "qemu/rcu.h"

hw/9pfs/virtio-9p-device.c

@@ -17,7 +17,6 @@
 #include "qemu/sockets.h"
 #include "virtio-9p.h"
 #include "fsdev/qemu-fsdev.h"
-#include "9p-xattr.h"
 #include "coth.h"
 #include "hw/virtio/virtio-access.h"
 #include "qemu/iov.h"