remove unused BOARD_USES_COMBINED_RECOVERY

Change-Id: I79520c510488d63d469b0d1a3a099420f7de1fe6
Remove the line that deletes *.rc from the recovery ramdisk.
This is no longer necessary since recovery init.rc only includes "import /init.recovery.${ro.hardware}.rc".

Fix up the unpackbootimg target.

Change-Id: I30b515bda982fbd944fffbc64501588cd3702dd8
build/core: Fix build due to commit cb74817

Change-Id: I40f1b8d21102f75ef2de9d44220b2d9654347a89