Remove ignoreSignature for cose signature checks

This flag is never used anywhere, so just remove it. When used, it would
bypass signature checks. This is something we generally don't want to
do, even in testing. So remove the flag so there's no temptation to use
it.

Bug: 190942528
Test: VtsHalRemotelyProvisionedComponentTargetTest
Change-Id: I0433c1eedc08e9a5a5ad71347154867dba61689e
Merged-In: I0433c1eedc08e9a5a5ad71347154867dba61689e