MIPS: Octeon: Delete built-in DTB pruning code for D-Link DSR-1000N.

Users will get more complete functionality by using the appended DTB,
so delete the legacy booting support for this board.

Signed-off-by: Aaro Koskinen <aaro.koskinen@iki.fi>
Cc: linux-mips@linux-mips.org
Cc: devicetree@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/13464/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>