build: don't clear recovery ramdisk

Clearing recovery ramdisk removes all files place there by the
device tree and all busybox symlinks placed there by recovery

Change-Id: I19e6164856a01a83a6e2c50ef96742edcb9f570f

Conflicts:
	core/Makefile
Merge branch 'lollipop' of github.com:AOSParadox/android_build into lollipop