macbook21: Kill empty mainboard.asl

Change-Id: I29c7d367df7d1ce911f6cd7ed5e5c56865b41dcc
Signed-off-by: Vladimir Serbinenko <phcoder@gmail.com>
Reviewed-on: http://review.coreboot.org/7063
Reviewed-by: Patrick Georgi <pgeorgi@google.com>
Tested-by: build bot (Jenkins)

src/mainboard/apple/macbook21/dsdt.asl

@@ -41,9 +41,6 @@ DefinitionBlock(
 	// General Purpose Events
 	#include "acpi/gpe.asl"
 
-	// mainboard specific devices
-	#include "acpi/mainboard.asl"
-
 	Scope (\_SB) {
 		Device (PCI0)
 		{