Removing unpack_bootimg from kernel build tools

After commit I48c9f6767cb7b2c3e3bead008e630eeef310fca3,
`certify_bootimg` no longer requires `unpack_bootimg`.
So no need to add `unpack_bootimg` into kernel build tools.

Bug: 226121398
Test: TH
Change-Id: Ib97b5b0075eb42d6b2d89e433fae376ba42d61f6
1 file changed