Revert "build: releasetools: ota: Add support for 32-64 bit upgrades"

* This was only required for tomato kitkat 32bit to lollipop 64bit
  migration. This is no longer a supported upgrade case, so revert
  it to be inline with AOSP.
* Users coming from stock should flash an updated 64bit recovery first

This reverts commit b8951067.

Change-Id: Iccf37e5292c2068e9a1f8aeb370719cd9ced8c44