[ARM] remove reference to non-existent MTD_OBSOLETE_CHIPS

The CONFIG variable MTD_OBSOLETE_CHIPS was deleted in commit
ba7cc09c9c9e29a57045dc5bbf843ac1cfad3283.

Signed-off-by: Robert P. J. Day <rpjday@crashcourse.ca>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

arch/arm/configs/collie_defconfig

@@ -367,7 +367,6 @@ CONFIG_MTD_CFI_UTIL=y
 # CONFIG_MTD_RAM is not set
 # CONFIG_MTD_ROM is not set
 # CONFIG_MTD_ABSENT is not set
-CONFIG_MTD_OBSOLETE_CHIPS=y
 CONFIG_MTD_SHARP=y
 # CONFIG_MTD_XIP is not set