linux-dtb.inc: drop unused DTB_NAME variable from do_install

* this is causing do_install to depend on KERNEL_IMAGE_BASE_NAME which in some cases contains something like BUILD_NUMBER from CI, that caused do_install to be reexecuted every single time, which is very sad to be caused by unused variable.
* jethro and newer don't need this change, because it's also fixed in commit 86b3f29f93e3f87903668ea317c6bd97be4cdf62
Author: Marek Vasut <[email protected]>
Date: Thu May 14 14:31:11 2015 +0200
Subject: kernel: Build DTBs early

---
 meta/recipes-kernel/linux/linux-dtb.inc | 1 -
 1 file changed, 1 deletion(-)

index 6b8f1a5..4779be2 100644
@@ -13,7 +13,6 @@ do_install_append() {
 				DTB=`basename ${DTB} | sed 's,\.dts$,.dtb,g'`
 			fi
 			DTB_BASE_NAME=`basename ${DTB} .dtb`
-			DTB_NAME=`echo ${KERNEL_IMAGE_BASE_NAME} | sed "s/${MACHINE}/${DTB_BASE_NAME}/g"`
 			DTB_SYMLINK_NAME=`echo ${KERNEL_IMAGE_SYMLINK_NAME} | sed "s/${MACHINE}/${DTB_BASE_NAME}/g"`
 			DTB_PATH="${B}/arch/${ARCH}/boot/dts/${DTB}"
 			oe_runmake ${DTB}

2.6.3