Remove BUSYBOX variable from ramdisk-defaults

ramdisk-defaults file is sourced before chroot to an image being created
is executed. Busybox path should be set inside chroot instead.

Change-Id: Ic0e1d3093ca9d489dd96b14157e93b336cf0baee

elements/ramdisk/post-install.d/99-build-ramdisk

@@ -19,6 +19,7 @@ FIRMWARE_DIR=$MODULE_ROOT/lib/firmware
 LIB_UDEV=$LIB_UDEV_ROOT/lib/udev
 INIT="$_LIB/scripts/init"
 FUNCTIONS_D="$_LIB/scripts/d"
+BUSYBOX=${BUSYBOX:-$(which busybox)}
 
 mk_build_dir
 mkdir -p $TMP_BUILD_DIR/mnt

lib/ramdisk-defaults

@@ -21,4 +21,3 @@ export DIB_MIN_TMPFS=${DIB_MIN_TMPFS:-1}
 source $_LIB/common-defaults
 MODULE_ROOT=${DIB_MODULE_ROOT:-""}
 LIB_UDEV_ROOT=${DIB_LIB_UDEV_ROOT:-""}
-BUSYBOX=${BUSYBOX:-$(which busybox)}