chardev: remove the headers of Memory chardev driver

Memory chardev driver is no longer used, and Commit:
4bf0bb80 has droped
it but the headers, so clean it up.

Signed-off-by: Lei Li <lilei@linux.vnet.ibm.com>
Message-id: 1366188414-24214-1-git-send-email-lilei@linux.vnet.ibm.com
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>