[S390] Remove tape block device driver.

Remove the tape block device driver. It's not of real use but has
already created some confusion when users wanted to access tape devices
and used the block device nodes instead of the character device nodes.

Also remove the whole tape documentation since it's completely outdated
and we have the device drivers book which is the place where everything
is properly documented.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>