Drop unused EXTERNAL_MRC_BLOB

The Kconfig variable EXTERNAL_MRC_BLOB is not used.
Drop it.

Change-Id: I3caa5c2b6bcf5d2c13b6987da8ab3987bad0e506
Signed-off-by: Stefan Reinauer <reinauer@google.com>
Reviewed-on: http://review.coreboot.org/3829
Tested-by: build bot (Jenkins)
Reviewed-by: Kyösti Mälkki <kyosti.malkki@gmail.com>

src/northbridge/intel/haswell/Kconfig

@@ -35,10 +35,6 @@ config VGA_BIOS_ID
 	string
 	default "8086,0166"
 
-config EXTERNAL_MRC_BLOB
-       bool
-       default n
-
 config CACHE_MRC_SIZE_KB
 	int
 	default 512

src/northbridge/intel/sandybridge/Kconfig

@@ -72,10 +72,6 @@ config VGA_BIOS_ID
 	string
 	default "8086,0166"
 
-config EXTERNAL_MRC_BLOB
-       bool
-       default n
-
 config CACHE_MRC_SIZE_KB
 	int
 	default 512