Move busybox binary-dep to ramdisk element

Busybox should be installed and managed from the ramdisk element,
since that is common to all elements that need busybox.  In
addition, we do not want busybox installed when building Dracut
ramdisks, so it can't be in the deploy-* elements.

Change-Id: I2656d20b466138f7f6dfcf558ba90c6909151d3c