[MTD] [MAPS] Remove flash maps for no longer supported 405LP boards

drivers/mtd/maps includes flash maps for the Beech and Arctic PowerPC
405LP based boards.  However, the 405LP was discontinued before any
quantity were distributed and those boards no longer have kernel
support in general.  Therefore, this patch removes this obsolete code.

Signed-off-by: David Gibson <dwg@au1.ibm.com>
Signed-off-by: David Woodhouse <dwmw2@infradead.org>