Remove Chestnut mtd map file.

The chestnut now sets up its MTD map from its platform-specific file so 
the map file drivers/mtd/maps/chestnut.c is no longer needed.  This 
patch removes the file & the Kconfig/Makefile hooks.

Please apply.

Signed-off-by: Mark A. Greer <mgreer@mvista.com>
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