MIPS: Kconfig: remove "config MIPS_DISABLE_OBSOLETE_IDE"

The Kconfig symbol MIPS_DISABLE_OBSOLETE_IDE was added in v2.6.10. It
has never been used. Let's remove it.

The symbol was originally introduced by the following commit

commit 2bfa662b64a7ee593f3039c1d3fd81a7766a63cd
Author: Pete Popov <ppopov@embeddedalley.com>
Date:   Tue Oct 12 06:24:19 2004 +0000
    - Db1550 bug fixes
    - updated defconfig
    - updated Kconfig to use DMA_COHERENT since new silicon is coherent

Signed-off-by: Paul Bolle <pebolle@tiscali.nl>
Patchwork: http://patchwork.linux-mips.org/patch/5064/
Acked-by: John Crispin <blogic@openwrt.org>