Switch from compos_verify_key to compos_verify

We no longer need to validate the public/private key files. Instead we
delegate signature checking to compos_verify.

(I've left the stub of the key checking in for, partly because
completely removing it will be a big change in its own right, and
partly to avoid merge conflicts.)

Bug: 218494522
Test: atest CompOsSigningHostTest CompOsDenialHostTest
Change-Id: I84e62c0f092e663fde78ac68766f922f58568e57
1 file changed