Revert "Add support for vendor_boot"

This reverts commit 7dfa4fd6797b41d2b02a55ac9f3f4f673cad59d9.

Reason for revert: go/flash issue on flashing vendor_boot

Bug: 152010460
Change-Id: I53c6c9a659c18d43fa7c529d75672d51d0619d2b
3 files changed