ota: Generate recovery-from-boot.p file

This may be wanted to update the recovery with system updates

Change-Id: Iacd41be7a8018cbc08b2606485d446756910f506
keys: avoid duplicating recovery keys

Setting PRODUCT_EXTRA_RECOVERY_KEYS duplicates the default key and
makes it so we can't set an extra key earlier in the build

Change-Id: I239d9994d9ad40b1779877ea2e89b55bd02e4c00
Revert "Allow devices to specify certain ro. props via TARGET_UNIFIED_DEVICE"

This reverts commit ea499153b11a32fa25311f07033496569c3045a6.

Conflicts:
	core/Makefile
	tools/releasetools/ota_from_target_files