Revert "ota: Validate any installed data's signature against our own"

* otasigcheck doesn't work on encrypted devices and makes
  the zip installation fail since oreo.
* The build part of this was never ported to oreo.

This reverts commit aff5e54c4ef5fec7e67e830f83ee64424005d07c.

Change-Id: I411f33c1db64844091c1692ef4706ae541925d4f
2 files changed