Remove participant verifiable capabilities #1823

Is your feature request related to a problem? Please describe.
When uss_qualifier was first developed, we speculated that regulators may want to conceptually build their top-level approval from approval of a larger set of smaller capabilities. For instance, U-space NetRID via ASTM F3411 requires basic F3411 compliance, but also compliance to a set of requirements that are otherwise optional in F3411. The U-space regulator could say "I think you're verified if you verify the 'basic F3411' capability plus the 'operator position sharing' capability plus ...". Now that uss_qualifier is somewhat mature as an approved means of verification for regulators (1.8M+ strategically-coordinated flights in the US), I think we can conclude that this is not the approach preferred by regulators. Instead, the "tested requirements" (referring to the uss_qualifier report artifact of that name) approach is preferred:

1. Participants construct a compliance matrix mapping regulator requirements to lower-level requirements like ASTM standard requirements, some of which uss_qualifier can verify compliance to
2. Participants construct a uss_qualifier test configuration with a "tested requirements" artifact that enumerates all the requirements annotated as "verified by automated testing" in their compliance matrix
3. Participants highlight the single "Requirement verification status" box to the regulator that is either green or not green indicating whether verification was confirmed, and regulators can check "which test" was performed by looking at the "Test baseline identifier".

Describe the solution you'd like
Remove the concept of participant verifiable capabilities from the codebase to reduce maintenance burden from an unused feature.

Describe alternatives you've considered
We would want to keep this feature if we anticipated it being useful, but I think the apparent regulator coalescence around the "tested requirements" approach suggests this is unlikely to be the case.