Remove device-specific bits if recovery_as_boot

On legacy devices (launched with R and below), if device:
- has a vendor_boot partition, and
- uses recovery_as_boot

Then, when building the recovery/boot partition, the
device-specific bits, including dtb/kernel base/pagesize should
be moved to vendor_boot.

Previously, it is incorrectly assumed that A/B => recovery_as_boot.
In reality, we do have A/B devices with a dedicated recovery partition.

Note that for devices that uses GKI (BOARD_USES_GENERIC_KERNEL_IMAGE),
recovery_as_boot is never set to true. Instead, recovery resources
are moved to vendor_boot. On these devices, the conditional
'vendor_boot && recovery-as-boot' is always false. Hence:

- If the device has a dedicated recovery partition, it should use V3 header,
  and dtb/base/pagesize won't be in recovery header.
- If device does not have a dedicated recovery partition, the recovery
  image won't be built.

Test: builds
Change-Id: I0db2af20470cbe8a21044a984cccf264590aaccf