net: remove the caif_hsi driver

The caif_hsi driver relies on a cfhsi_get_ops symbol using symbol_get,
but this symbol is not provided anywhere in the kernel tree.  Remove
this driver given that it is dead code.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: David S. Miller <davem@davemloft.net>